UC-NRL 


B    3    mi 


ering 


Molded 
Electrical    Insulation 

and 

Plastics 


By 

EMILE  HEMMING 


New  York 

WARD  CLAUSEN  CO.,  PUBLISHERS 
200  FIFTH  AVENUE 

1914 


COPYRIGHT  1914 
BY  EMILE  HEMMING 

ALL    RIGHTS    RESERVED 


Tk  3 


Engineering^ 
Library 


TABLE  OF  CONTENTS 


Introduction 5 

What  Is  Molded  Insulation? 7 

Molded  Insulation  Ten  Years  Ago 9 

Classification  of  Molded  Insulation  Used  To-day 16 

Raw  Materials,   etc 20 

Hot  Molded  Organic  Materials (Class  '  'A") . .  66 

Cold  Molded  Organic  Materials (Class  '  'B") . .  71 

Cold  Molded  Inorganic  Materials (Class  '  <C") . .  73 

Ceramics,    Porcelain    (Class  "D")  .  .  75 

Rubber  Compounds (Class  '  *E") .  .  78 

Organic  Plastics   (Class  "F") . .  79 

Synthetic  Resinous  Materials (Class  "G") . .  '    85 

Fibre  Sheet  Materials   (Class  '  'H") .  .  90 

Molded   Mica (Class    "F ') . .  92 

Properties 93 

Molds  and  Dies  110 

Illustrations  of  Molded  Pieces 135 

Laboratory  Tests    172 

Dielectric  Strength  Tests  175 

Insulation  Resistance  Tests 184 

Tensile  Strength  Tests   189 

Arc  Tests    .  190 


INTRODUCTION 


INTRODUCTION 


About  ten  years  ago  a  leading  electrical  concern  in 
Europe  sent  one  of  its  engineers  on  an  extended  trip  to 
America  for  the  purpose  of  studying  and  reporting  the 
progress  made  in  the  field  of  molded  insulation  for  elec- 
trical purposes. 

Having  had  full  access  to  the  works  of  the  large 
manufacturing  concerns,  and  after  careful  study  of  con- 
ditions, the  engineer  returned  home  and  reported  that  the 
state  of  the  art  in  this  field  was  about  the  same  in  both 
countries. 

Since  then  a  series  of  new  inventions  in  the  field  of 
electrical  insulation  products  have  been  developed  and 
enormous  progress  has  been  made. 

While  electrical  engineers  have  been  kept  some- 
what informed  of  these  new  inventions  and  products 
through  the  medium  of  technical  periodicals  and  ad- 
vertisements, yet  no  book  has  been  published  dealing 
in  an  entire,  comprehensive  and  unbiased  manner  with 
'he  developments  in  this  art. 

This  subject  of  molded  insulation  is  one  of  great 
and  growing  importance  in  almost  every  branch  of  elec- 
trical art.  A  few  years  ago  the  choice  of  insulating 
materials  lay  practically  between  porcelain,  hard  rubber, 
and  the  so-called  shellac  compounds,  but  to-day  a  con- 
siderable number  of  substances  of  widely  different  prop- 
erties and  constituents  are  offered  on  the  market. 


6  MOLDED    INSULATION 

The  purpose  of  this  book,  therefore,  is  to  deal 
thoroughly  and  as  briefly  as  possible  with  the  progress 
in  the  field  of  molded  insulation,  to  trace  its  develop- 
ment during  the  last  ten  years,  and  to  discuss  its  present 
status:  to  treat  of  the  important  basic  principles  of  the 
new  products  and  inventions,  omitting  specific  trade 
names;  to  give  the  engineer  an  insight  into  materials  and 
methods  employed  in  manufacture,  disclosing  various 
characteristics,  both  favorable  and  unfavorable;  and  so 
to  guide  him  to  a  proper  selection  of  the  substances  best 
suited  to  his  wants  and  requirements. 

I  will  try  to  explain  in  a  short,  practical  way,  how 
out  of  hundreds  of  new  products  which  have  appeared  on 
the  market,  and  for  which  great  claims  have  been  made 
by  inventors  and  experimenters,  only  a  few  have  stood 
up  and  survived  under  operating  conditions;  and  how 
these  have  contributed  to  electrical  progress. 

Never  before  has  the  interest  of  the  electrical  en- 
gineer been  so  keen  as  to  what  type  of  insulating  parts 
to  use  in  his  machine  or  apparatus  as  at  present,  and  I, 
therefore,  express  the  hope  that  this  short  treatise  may 
be  a  helpful  guide  and  of  particular  interest  to  him. 


EMILE  HEMMING. 


Passaic,  N.  J.,  U.  S.  A. 
April,  1914. 


WHAT  IS  MOLDED  INSULATION  ? 


WHAT  IS  MOLDED  INSULATION? 


The  term  "Molded  Insulation"  is  applied  to  that 
class  of  mechanical  elements  of  electrical  apparatus  used 
for  insulating  purposes.  These  elements  are  formed  of 
a  plastic  mass  in  molds  or  dies,  usually  under  pressure. 

This  plastic  mass  is  composed  fundamentally  of  two 
elements,  viz:  a  binder,  and  a  filler.  Both  organic  and 
inorganic  binders  and  fillers  are  used. 

When  the  binder  is  organic  the  mixture  depends 
upon  it  principally  for  its  insulating  qualities,  and  the 
filler,  while  it  may  have  an  insulating  value,  is  used 
either  to  make  the  mixture  cheaper  or  because  of  its 
mechanical  or  physical  properties. 

Inorganic  binders  are  used  primarily  to  produce 
materials  capable  of  withstanding  greater  heat  than  the 
organic;  they  sometimes  not  only  act  in  the  capacity  of 
a  binder,  but  enter  into  combinations  of  a  mechanical 
or  chemical  nature  with  the  fillers, 

In  the  early  days,  makers  of  electrical  apparatus 
used  for  insulating  purposes  such  materials  as  were  found 
at  hand.  Of  these  slate,  marble,  wood  and  mica  were 
found  to  be  best  suited  for  the  respective  purposes.  The 
•demand  for  a  material  which  could  be  more  readily 
shaped  into  complicated  forms  soon  added  porcelain, 
hard  rubber  and  fibre  to  the  list. 

These  three  manufactured  products  were  early 
adopted  as  standards.  Their  properties  are  well  known 
and  the  characteristics  of  the  output  of  the  various 


8  MOLDED    INSULATION 

makers  differ  from  each  other  in  only  a  comparatively 
slight  degree. 

The  progress  made  in  the  construction  of  electrical 
machinery  and  appliances  very  soon  created  a  demand 
for  other  materials  which  would  embody  the  desirable 
features  of  these  substances  and  also  possess  qualities 
which  they  lacked.  This  demand  has  given  being  to  a 
very  diversified  group  of  products  which  are  classified 
under  the  title  given  this  book. 

All  kinds  of  materials  are  commonly  referred  to 
under  the  general  term  of  "COMPOSITION."  Molded 
Insulation  embraces  a  great  variety  of  products  differ- 
ing widely  in  their  characteristics  as  well  as  in  their 
constituent  elements;  and  because  of  the  newness  of  this 
art  and  because  of  the  secrecy  maintained  by  the  manu- 
facturers, engineers  are  by  no  means  as  well  informed 
of  the  nature  of  these  products  as  they  should  be. 

These  newer  materials  are  so  rapidly  coming  into 
extensive  use  that  it  is  highly  important  that  they  be 
properly  classified  and  that  their  characteristics  be 
thoroughly  understood  by  electrical  engineers  and 
designers. 

I  will,  therefore,  try  to  classify  into  standard  cate- 
gories all  the  so-called  molded  compositions  developed 
up  to  the  present  time,  especially  those  which  have  been 
most  generally  adopted  by  electrical  manufacturers. 


MOLDED  INSULATION  TEN    YEARS  AGO       9 


MOLDED    INSULATION    TEN    YEARS    AGO 


Ten  years  ago  the  molded  insulating  material  most 
-widely  used  was  porcelain.  It  was  practically  the  only 
^fireproof  material  known  at  the  time.  Its  high  dielectric 
-strength,  when  properly  made,  its  waterproof  qualities 
and  its  low  cost  made  it  indispensible  for  a  great  many 
uses. 

Owing,  however,  to  its  brittleness,  it  was  unsuitable 
for  many  purposes,  and  electrical  engineers  and  con- 
structors employed  vulcanzied  fibre  or  wood  impreg- 
nated with  oil  to  a  considerable  extent. 

Hard  rubber  was  also  much  used  as  an  electrical 
insulator,  either  as  such  or  as  a  binder  in  materials 
having  asbestos  or  other  mineral  substances  as  fillers. 
These  so-called  vulcanized  asbestos  materials,  com- 
posed of  asbestos  fibre  with  rubber  as '  a  binder, 
were  molded  into  the  required  shapes  and  then 
vulcanized.  They  were  excellent  in  every  respect  except 
price  and  the  inability  of  rubber  to  withstand  any  con- 
siderable degree  of  heat. 

In  the  writer's  opinion  these  products  constituted 
the  best  molded  materials  produced  up  to  that  time/ but 
the  steadily  increasing  price  of  rubber  made  the  cost  of 
articles  of  this  material  prohibitive  for  many  purposes, 
and  gave  rise  to  many  substitutes,  some  of  which  came 
into  extensive  use.  I  refer  especially  to  the  so-called 
shellac  compounds,  based  principally  on  the  use  of  shellac, 


10  MOLDED    INSULATION 

asphalt,  rosin  and  other  gums  as  binders  for  asbestos,  or 
other  fillers. 

These  shellac  materials  were  all  molded  in  heated 
dies  and  cooled  before  being  removed  therefrom  as  a 
finished  product,  which  is  a  method  of  manufacture  much 
cheaper  and  simpler  than  the  somewhat  lengthy  process 
of  vulcanization  so  necessary  when  rubber  is  employed 
and  one  of  the  chief  reasons  for  the  wide  popularity  of 
materials  of  this  character. 

Numerous  attempts  have  been  made  in  the  last  ten 
years  to  utilize  alkaline  silicates  as  binders  for  asbestos 
and  other  fillers.  They  make  good  binders,  but  on  ac- 
count of  their  inability  to  resist  the  softening  influence 
of  moisture,  various  processes  were  developed  to  render 
them  insoluble.  These  depend  on  the  use  of  lime  com- 
pounds, aluminates,  etc.,  and  while  it  was  found  pos- 
sible to  convert  the  silica  into  an  insoluble  form,  other 
products  of  reaction  were  always  present,  which  were  just 
as  readily  acted  upon  by  moisture.  Further,  in  many 
cases  the  silicate  compounds  formed  were  found  to  be 
acted  upon  by  some  of  the  other  components,  so  that  dis- 
integration eventually  occurred.  This  class  of  materials 
has,  therefore,  practically  disappeared. 

Another  material,  and  one  of  more  promise,  employed 
hydraulic  cement  and  water  mixed  with  asbestos  fibre. 
It  was  formed  into  thin  sheets  on  a  machine  similar  to  a 
paper-making  machine  and  as  many  of  these  sheets  were 
built  up  as  were  necessary  to  obtain  the  desired  thick- 
ness. These  sheets  were  cut  to  size,  the  pieces  placed 
into  molds  and  held  under  pressure  until  the  hydraulic 
cement  had  undergone  preliminary  or  initial  set.  Such 
a  material,  while  somewhat  hygroscopic,  is  still  very 
stable  and  improves  rather  than  deteriorates  with  age  and 
climatic  exposure.  This  and  other  desirable  character- 


MOLDED  INSULATION  TEN  YEARS  AGO     11 

istics  have  stimulated  experiments  with  this  type  of  sub- 
stances, and  great  progress  has  been  made  in  the  manu- 
facture of  molded  insulation  from  materials  of  this  nature. 
The  greatest  drawback  to  these  early  products  obtained 
by  the  above  process  was  that  it  was  not  possible  to  mold 
them  in  any  but  very  simple  forms,  and  they  were  not 
made  to  any  extent  except  in  flat  pieces. 

Mica  built  up  into  sheets  or  formed  into  shapes  was 
in  general  use.  In  this  connection  no  basic  improve- 
ments have  been  made,  although  a  great  many  experi- 
menters have  tried  to  substitute  a  fireproof  or  at  least 
a  more  heat-resisting  binder  for  shellac. 

Several  patents  have  been  issued  and  considerable 
literature  has  been  published  relating  to  synthetic 
resinous  products  obtained  by  the  condensation  of  a  mix- 
ture of  phenol  and  formaldehyde.  Such  resin-like  sub- 
stances were  intended  to  be  a  substitute  for  the  natural 
resinous  binders  in  the  so-called  shellac  compositions. 
These  products  were  produced  in  an  experimental  way, 
but  with  indifferent  commercial  success  and  were  little 
heard  of  for  several  years. 

The  desirability  of  a  material  which,  when  properly 
made,  would  have  the  easy  molding  properties  of  the 
shellac  materials,  and  in  addition  possess  the  great  heat- 
resisting  qualities  and  dielectric  strength  which  these 
new  synthetic  products  promised,  promoted  their  rapid 
development,  so  that  to-day  such  materials  are  success- 
fully manufactured  and  are  unsurpassed  for  certain 
purposes. 

Another  product  of  which  great  success  was  ex- 
pected was  a  composition  of  ox  blood  and  wood  pulp 
molded  in  hot  dies  in  a  manner  similar  to  the  shellac  com- 
pounds. This  material  was  obtained  by  treating  the  blood 
to  obtain  its  fibrine.  This  was  then  dried  and  powdered 


12  MOLDED   INSULATION 

and  mixed  with  the  filling  materials.  The  mass  was  then 
subjcted  to  hydraulic  pressure  in  hot  closed  dies. 

The  binding  qualities  of  the  fibrine  and  consequently 
the  tensile  strength  of  the  product  was  sometimes  in- 
creased by  the  addition  of  glutinous  or  resinous  sub- 
stances. One  process  employed  wood  pulp  having  a  large 
resin  content,  which  under  heat,  united  with  the  fibrine 
to  cement  the  mass  more  thoroughly. 

Perfectly  molded  articles  of  this  type  possessing 
higher  heat-resisting  properties  than  the  shellac  ma- 
terials were  made  and  used  to  quite  a  considerable  extent 
for  telephone  receivers  and  similar  work;  but  due  to  the 
fact  that  it  is  not  as  readily  molded  or  as  chemically 
stable  as  shellac,  its  use  has  rather  decreased  than  in- 
creased within  the  last  ten  years. 

An  entirely  different  material  which  has  found  more 
extensive  use  in  the  domestic  purposes  than  in  the  elec- 
trical arts  was  formed  of  casein,  chemically  treated  to 
convert  it  into  a  hard,  tough  substance.  This  material 
can  be  easily  molded  and  worked  with  tools,  but  on  ac- 
count of  its  inability  to  withstand  moisture,  its  useful- 
ness for  electrical  purposes  is  limited. 

An  attempt  was  made  in  England  to  manufacture  a 
product  employing  sulphur  as  a  binder  for  organic  and 
inorganic  materials,  but  after  a  few  years  of  unsuccessful 
operation  the  company  failed.  This  process  was  fore- 
doomed to  failure  at  the  start,  for  it  has  long  been  known 
that  metallic  parts  embedded  in  hard  rubber  containing 
excess  of  sulphur  were  energetically  attacked  by  the  acids 
resulting  from  oxidation  of  the  sulphur,  and  for  this  and 
other  reasons  this  material  lasted  only  until  a  superior 
article  appeared. 

Several  attempts  have  been  made  to  use  the  waste 
from  the  manufacture  of  horn  and  hoof  products  by 


MOLDED  INSULATION  TEN  YEARS  AGO     13 

dissolving  or  at  least  agglomerating  it  by  some  patented 
or  secret  process  and  afterward  welding  under  heat  and 
pressure.  These  processes  were  a  total  failure.  The 
idea  originated  from  the  use  of  these  materials  in  the 
manufacture  of  buttons,  hair  ornaments  and  the  like, 
and  several  factories  were  started  simultaneously  in 
Europe  as  well  as  in  this  country  to  place  materials  of 
this  character  on  the  market,  and  samples,  accompanied 
by  glowing  prospectuses,  appeared;  but  the  samples, 
after  a  few  months'  exposure  to  the  atmosphere,  under- 
went such  physical  and  chemical  changes  as  to  demon- 
strate their  unfitness  for  electrical  purposes. 

The  process  of  manufacture  was  to  reduce  the 
cleaned  raw  materials  to  a  powder  and  to  compress  this 
powder  in  hot  dies.  If  the  material  had  then  become 
sufficiently  plastic  to  mold  properly,  and  if  it  had  coal- 
esced under  heat  and  pressure,  it  might  have  had  a  hap- 
pier history,  but  unfortunately  it  was  found  necessary 
to  mix  with  it  such  reagents  as  hydrocholoric  and  sul- 
phuric acids,  calcium  chlorate,  various  alkalies,  etc.,  to 
dissolve,  agglomerate  or  to  decompose  the  powder  and 
render  it  plastic ;  and  owing  to  the  nature  of  the  chemicals 
employed  and  their  imperfect  combination  with  the  horny 
substance,  the  resultant  products  were  very  unstable. 

Papier  Mache  formed  into  various  shapes  has  been 
widely  used  both  here  and  abroad.  Such  products  were 
made  by  sticking  together  sheets  of  especially  prepared 
stiff  paper,  by  means  of  glutinous  substances,  and  placing 
the  prepared  sheets  in  wood  or  metal  forms  to  produce 
the  desired  shapes.  These  were  placed  in  ovens  until  the 
whole  mass  became  dry  and  hard.  The  pieces  were  then 
coated  with  varnishes  made  of  asphalt  and  resin  dissolved 
in  linseed  oil  or  other  suitable  solvents,  and  again  placed 
in  the  ovens.  By  this  means  the  insulating  varnishes  were 


14  MOLDED    INSULATION 

made  to  penetrate  the  surface  layers  of  the  paper. 

This  process  was  repeated  until  the  paper  became 
covered  with  a  hard,  tough,  waterproof,  insulating  sur- 
face. As  the  varnishes  employed  were  the  principal 
insulating  elements,  it  is  obvious  that  the  quality  of  the 
product  depended  on  them. 

Such  materials  are  well  adapted  to  the  manufacture 
of  bobbins,  large  switch  box  covers  having  thin  walls,  and 
similar  parts  which  it  would  be  difficult  to  mold  of 
plastic  materials,  and  they  are  still  used  to  a  considerable 
extent.  Such  articles  are  flexible,  very  tough  and  fairly 
good  insulators. 

Another  form  of  material  which  has  practically  dis- 
appeared employed  cabinet  makers'  glue  as  a  binder  for 
vegetable  or  mineral  fillers.  The  glue  was  mixed  with 
the  powdered  fillers  and  molded  in  heated  dies  or  rolled 
in  sheet  form,*and  the  sheets  were  cut  to  the  required 
size  and  molded  in  a  heated  condition.  The  products 
were  generally  treated  with  formaldehyde,  chromates  or 
other  chemical  agents  to  render  the  glue  waterproof  and 
chemically  stable.  No  process,  however,  was  developed 
which  would  make  animal  glue  permanently  waterproof 
and  stable. 

Attempts  were  made  to  produce  a  molded  insulat- 
ing material  by  treating  cellulose  and  celluloid  in  a  num- 
ber of  different  ways  to  reduce  their  inflammability,  but 
while  these  materials  had  great  success  in  other  indus- 
tries, they  were  of  no  great  value  as  electrical  insulators. 

Numerous  attempts  were  made  to  use  paraffine  and 
vegetable  waxes  as  binders,  but  these  materials  were  of 
short  popularity  due  to  their  low  melting  points. 

Efforts  were  made  to  use  the  waste  of  slate  and 
marble  works  by  reducing  it  to  a  fine  powder,  mixing 
it  with  proper  binders,  and  molding  under  heat  and  pres- 


MOLDED  INSULATION  TEN  YEARS  AGO     15 

sure ;  the  resulting  products  resembled  the  natural  slate 
and  marble,  but  while  such  materials  are  still  made  to 
some  extent,  their  use  is  diminishing. 

Another  class  of  materials  employing  a  vege- 
table gluten  for  a  binding  medium  was  composed  of 
starch  or  dextrines,  and  vegetable  or  mineral  fibres. 
After  being  molded  and  dried,  the  parts  were  impreg- 
nated with  mineral  or  vegetable  waxes.  Fairly  stable 
materials  were  thus  obtained,  but  to-day  these  products 
are  only  a  memory. 

A  material  was  made  of  the  powdered  waste  of 
soapstone  by  mixing  it  with  suitable  binders  and  firing 
the  molded  parts  somewhat  after  the  manner  of  porcelain 
Such  products  are  still  in  use  and  further  reference  to 
them  will  be  made  in  another  chapter. 

Turf  has  attracted  considerable  attention  for  molded 
insulation  experiments  due  to  its  low  cost,  its  wide  dis- 
tribution and  fibrous  nature.  Turf  materials  made  with 
asphaltic  or  resinous  binders  were  in  practical  use  for 
some  time,  but  have  almost  entirely  disappeared  owing 
to  their  poor  heat-resisting  qualities. 

The  following  chapters  will  deal  with  ,  molded 
insulating  materials  employed  to-day,  including  such  of 
the  above  mentioned  early  ones  as  are  still  in  practical 
use,  and  eliminating  those  which  have  been  abandoned. 


16  MOLDED    INSULATION 


CLASSIFICATION  OF  MOLDED  INSULATION  USED 

TO-DAY 


Molded  insulating  materials  may  be  broadly  grouped 
into  the  following  classes : 

CLASS  "A"— ORGANIC  HOT  MOLDED  MATERIALS 

Materials  obtained  by  mixing  natural  organic  binders 
with  organic  or  inorganic  fillers,  thus  mechanically  com- 
bining the  fillers  with  the  plastic  binders,  molding  the 
mixtures  in  heated  'dies,  cooling  the  dies  and  removing* 
the  pieces  from  the  molds  in  a  finished  condition. 

CLASS  "B"— ORGANIC  COLD  MOLDED  MATERIALS 

Materials  obtained  by  mixing  organic  binders  in  a 
dissolved  condition  with  organic  or  inorganic  fillers, 
molding  in  a  cold  state  and  hardening  after  removal  from 
the  molds. 

CLASS    "C"— INORGANIC    COLD    MOLDED 
MATERIALS 

Materials  obtained  by  mixing  inorganic  binders, 
chiefly  with  inorganic  fillers,  molding  in  a  cold  state  and 
solidifying  after  removal  from  the  dies. 

CLASS  '^"—CERAMICS 

Ceramics,  known  generally  under  the  name  of 
"Porcelain,"  made  from  a  mixture  of  China  clay,  silica 


CLASSIFICATION  OF  MOLDED  INSULATION  17 

and  water,  molded  in  a  cold  state  and  heated  to  a  fusing 
point  after  removal  from  the  dies. 


CLASS  "E"— RUBBER  COMPOUNDS 

Mixtures  of  rubber  or  gutta  percha  generally  adulter- 
ated with  asphalts,  oils  and  other  substitutes,  mixed  with 
inorganic  fillers  and  vulcanized  by  well-known  processes 
with  sulphur. 


CLASS  "F"— ORGANIC  PLASTICS 

Materials  made  from  organic  substances  chemically 
treated  to  render  them  plastic,  and  molded  into  the  de- 
sired forms.  This  class  embraces  a  wide  range. 


CLASS  "G"— SYNTHETIC  RESINOUS  PRODUCTS 

Materials  obtained  by  mixing  synthetic  organic 
binders  with  organic  or  inorganic  fillers,  and  molding 
the  mixtures  in  heated  dies. 


CLASS  "H"— HARDENED  FIBRE  MATERIALS 

Materials  made  from  paper  treated  in  such  a  way 
as  to  render  them  hard.  The  molding  of  this  class  is 
practically  limited  to  the  production  of  sheets,  rods  and 
tubes. 


18  MOLDED    INSULATION 

CLASS  "I"— MOLDED  MICA 

The  qualities  of  these  different  products  vary  widely 
and  there  is  no  one  insulating  material  made  to-day 
which  fulfills  all  the  requirements  demanded  by  the 
various  electrical  applications. 

Some  manufacturers  claim  their  pro'ducts  to  be 
suited  to  all  applications,  but  this  is  decidedly  not  so. 
For  instance,  while  the  materials  of  Class  "D"  are  fire- 
proof, waterproof  and  inert  under  all  climatic  influences, 
their  use  is  limited  to  such  purposes  as.  do  not  require 
accuracy  of  dimensions  or  great  mechanical  strength. 
While  materials  made  under  Classes  "A,"  "B,"  "C," 
"E,"  "F"  and  "G,"  on  the  other  hand,  can  be  molded 
more  or  less  to  true  sizes  and  are  mechanically  strong, 
they  are  not  as  proof  against  climatic  conditions  as 
materials  of  Class  "D." 

The  electrical  engineer  has,  therefore,  to  use  his 
own  judgment  as  to  the  insulator  he  should  choose  for 
his  own  particular  needs,  and  fortunately  he  has  at  his 
disposal  numerous  different  materials  from  which  he  may 
make  proper  selection. 

While  the  manufacture  of  molded  insulation  is  a 
comparatively  new  art  and  much  further  progress  may 
be  confidently  expected  in  the  next  few  years,  it  has 
already  developed  to  a  point  where  the  products  of  the 
various  makers  are  divided  into  well  defined  classes 
which  have  been  on  the  market  and  under  the  test  of 
actual  service  conditions  for  a  long  enough  period  to 
enable  the  engineer  to  determine  which  make  of  material 
is  best  suited  to  his  needs. 

The  manufacture  of  molded  insulation  is  broadly 
speaking  not  a  complicated  art.  It  involves  a  few  well 
defined  steps  such  as  the  preparing  of  raw  materials, 


CLASSIFICATION  OF  MOLDED  INSULATION  19 

mixing,  molding  and  finishing,  but  as  is  true  with  many 
other  apparently  simple  processes  it  requires  long  ex- 
perience to  produce  satisfactory  results. 

A  proper  selection  of  raw  materials  is,  of  course, 
the  first  step,  but  manipulation  of  the  material  through 
all  its  stages  of  manufacture  requires  an  intimate  knowl- 
edge of  seemingly  unimportant  detail.  Thus  the  amount 
of  pressure  employed  and  the  speed  with  which  it  is  ap- 
plied in  the  molding  process  has  a  very  great  influence 
on  the  character  of  the  finished  product.  Two  pieces 
having  the  same  ingredients  and  subjected  ap- 
parently to  the  same  treatment,  while  they  may  be  alike 
in  appearance,  may  vary  in  their  behavior  in  use.  Too 
little  pressure,  too  great  pressure,  or  pressure  improperly 
applied  will  produce  an  article  of  poor  mechanical 
strength,  and  of  low  electrical  resistance,  and  so  on 
through  the  various  other  steps  of  manufacture. 

Before  going  into  further  detail  of  these  various 
classes,  I  will  discuss  briefly  the  raw  materials  em- 
ployed ;  explaining  their  derivation,  characteristics,  and 
their  properties  which  render  them  valuable  in  the  manu- 
facture of  molded  insulation. 


20  MOLDED   INSULATION 


RAW  MATERIALS 

ASBESTOS 

Chemically,  asbestos  is  a  silicate  of  magnesia  of 
fibrous  structure.  It  is  mined  principally  in  Canada, 
Russia.  South  Africa  and  Italy.  It  is  generally  known 
as  a  mineral  fibre,  supposed  to  be  fireproof  and  acid- 
proof.  Owing  to  these  properties  it  is  the  most  widely 
used  element  in  the  manufacture  of  molded  insulation 
to-day. 

The  term  "Asbestos,"  however,  is 'broadly  applied 
to  various  groups  of  crystalline  minerals  of  fibrous  struc- 
ture, and  while  they  are  not  affected  by  the  momentary 
exposure  to  heat,  a  continuous  temperature  of  above  900 
degrees  C.  w^ill  affect  this  material  so  that  it  loses  its 
chief  and  most  valuable  physical  characteristic,  namely, 
its  fibrous  structure. 

Mineralogically  asbestos  is  divided  into  three  prin- 
ciple classes,  namely,  Serpentine,  Antophyllite  and  Am- 
phibole.  Each  of  these  groups  is  sub-divided  into  several 
classes. 

I  refer  any  one  particularly  interested  in  the  prop- 
erties of  these  materials  to  the  very  excellent  publication 
of  the  Department  of  Mines,  Canada,  on  the  subject,  than 
which  no  better  and  more  precise  publication  has  yet 
been  issued. 

The  variety  which  is  of  interest  to  us  in  connection 
with  molded  insulation  is  the  Serpentine  class,  especially 
in  its  chrysolyte  form,  and  I  believe  the  chemical  analysis 
and  a,  short  description  of  this  variety  will  not  be  out  of 
place  here. 


RAW   MATERIALS  21 

The  composition  of  asbestos  varies  according  to  the 
location  of  the  mines,  but  the  following  table  gives  the 
average  composition  of  the  qualities  generally  used  in 
the  manufacture  of  molded  insulation. 

Silica    (Si02) 39.8 

Magnesia    (MgO) 41.4 

Lime    (CaO) 79 

Ferrous  Oxide    (FeO) 1.61 

Alumina    (A1208) i-07 

Moisture    (11,0) 15.33 

The  specific  gravity  varies  from  2.1  to  2.7, 

This  class  of  asbestos  should  not  be  termed  acid- 
proof,  as  it  is  more  or  less  attacked  even  by  weak  acids 
as  well  as  by  alkalies. 

There  are  several  varieties  of  asbestos  which  are  acid- 
proof,  but  their  physical  properties  are  not  the  same  as 
the  Serpentine,  inasmuch  as  the  acid-proof  asbestos  is 
generally  not  of  fibrous  structure,  although  some  acid- 
proof,  well  cleaned,  fibrous  asbestos  obtained  in  Canada 
and  Africa  is  to  be  found  in  the  market ;  but  the  very  high 
cost  of  such  asbestos  makes  it  prohibitive  for  use  in 
molded  insulation. 

Some  manufacturers  of  molded  insulation  claim  their 
products  to  be  acid-proof,  basing  their  claims  on  the 
acid-resisting  qualities  of  organic  binders  as  well  as  on 
the  supposed  acid-proof  qualities  of  the  asbestos. 

I  would,  however,  caution  against  the  use  of  molded 
insulation  containing  asbestos  as  a  filler  for  purposes 
where  the  product  has  to  withstand  the  action  of  acids 
or  alkalies. 

While  it  is  true  that  by  intimately  mixing  asbestos 
fibre  with  organic  binders  the  former  may  be  impreg- 
nated or  coated,  rendering  the  asbestos  fibre  itself  tern- 


22  MOLDED   INSULATION 

porarily  acid-resisting,  it  will  inevitably  succumb  to  the 
action  of  the  acid  in  the  course  of  time. 

Asbestos  has  been  of  great  importance  in  the  de- 
velopment of  molded  insulation  in  the  last  ten  years  and 
without  it  the  enormous  progress  made  could  not  have 
been  effected.  Its  fibrous  structure,  no  matter  how  short 
the  fibres,  gives  the  necessary  mechanical  strength  and 
flexibility,  without  which  the  binders  in  molded  insula- 
tion would  fail. 

Its  fire-resisting  qualities  prevent  the  arc  from  readily 
affecting  the  organic  binders,  unless  the  latter  should  be 
in  too  great  an  excess  in  the  composition. 

Asbestos  in  any  composition  is  entirely  inert  toward 
climatic  conditions,  with  the  exception  that  it  absorbs 
water  or  other  fluids.  This  property  renders  it  valuable, 
enabling  it  to  absorb  the  organic  binders,  and  through  the 
high  pressure  used  in  molding  these  asbestos  compounds, 
the  fibre  is  so  intimately  welded  and  united  that  the 
absorption  of  water  under  these  conditions  is  practically 
nihil.  This  is  especially  the  case  when  the  amount  of 
binder  exceeds  the  impregnating  capacity  of  the  asbestos. 
While  alone,  it  would  be  of  limited  use  as  an  electrical 
insulator,  as  it  readily  absorbs  moisture  from  the  air  and 
would,  therefore,  possess  no  insulating  properties.  Com- 
bined in  proper  manner  with  binders  it  is  one  of  the  most 
useful  elements  in  molded  insulation. 


CLAY 

Clays  are  of  importance  in  insulation  manufacture, 
being  the  principal  raw  materials  of  porcelain.     For  this 


RAW   MATERIALS  23 

purpose  clay  must  possess  fineness  of  grain,  freedom  from 
flint  and  other  impurities,  and  in  addition  to  silica  and 
alumina  as  its  essential  ingredients  must  contain  what 
are  known  as  fluxes.  The  fluxes  commonly  employed 
are  lime,  magnesia, N  soda,  and  potash.  They  occur  in 
clays  in  varying  amounts.  The  function  of  the  fluxes 
is  to  unite  with  the  silica  and  alumina,  forming  fusible 
bodies,  which  enable  the  pieces  to  be  vitrified  when  fired. 
Many  clays  are  quite  deficient  in  these  fluxes  and  to 
these,  therefore,  fluxes  containing  the  necessary  in- 
gredients are  added.  Other  materials  are  added  to  de- 
crease shrinkage  during  the  firing  process,  the  most 
common  of  these  being  sand  of  a  pure  grade. 

One  of  the  uses  of  clay  in  connection  with  electrical 
insulation,  which,  however,  is  of  lesser  importance,  is 
as  a  raw  material  for  the  manufacture  of  Portland 
Cement.  In  certain  sections  of  the  world  vast  quantities 
of  clay  are  so  used,  the  clay  supplying  the  silica,  iron 
oxide  and  alumina,  while  limestone  supplies  the  necessary 
lime  ingredients.  For  this  purpose  the  purity  and  physi- 
cal structure  of  the  clay  are  of  minor  importance,  the 
essential  being  that  the  silica  content  be  from  two  to 
three  times  the  content  of  combined  iron  oxide  and 
alumina. 


MICA 

Mica  is  a  mineral  of  peculiar  characteristic  striated 
form  and  is  of  prime  importance  in  the  electrical  arts, 
because  it  may  almost  be  called  a  perfect  insulator  in 
its  crude  or  natural  state. 

It  is  mined  chiefly  in  Canada,  the  United  States, 
India,  and  Siberia,  and  is  found  in  sheets  of  laminated 


24  MOLDED   INSULATION 

blocks  which  readily  split  up  into  thin  sheets  along  the 
axis.  Its  principal  use  is  for  electrical  insulating  pur- 
poses, for  in  addition  to  its  high  dielectric  strength  it 
possesses  great  heat-resisting  qualities  and  is  chemically 
inert  under  ordinary  conditions,  it  is  waterproof  and 
acid  proof;  and  these  properties  combined  with  its  great 
flexibility  make  it  an  ideal  insulating  material  for  many 
purposes. 

Chemically  it  is  a  Silicate  of  Aluminum  and  Mag- 
nesium combined  with  smaller  percentages  of  Potassium 
or  sodium  and  iron. 

An  analysis  of  a  kind  of  mica  as  used  for  electrical 
insulation  shows  it  to  be  composed  of: 

Alumina    (A12O3) 20.43 

Silica    (Si02) 41.18 

Potassium    (K) 8.35 

Iron  Oxide    (FeO) ..  . . 6. 

Manganese   (MnO) 2. 

Magnesium  Oxide    (MgO) 19.04 

Water  and  other  matters  (HF— H20) 3. 

Oil  somewhat  reduces  its  insulating  value.  While  mica 
in  its  natural  state  is  an  excellent  insulator,  its  tendency 
to  split  under  stress  or  manipulation  renders  it  necessary 
in  most  cases  to  subject  it  to  some  re-inforcing  treat- 
ment. This  is  done  by  separating  the  mica  into  sheets 
as  thin  as  possible  and  cementing  them  together  with 
resinous  binders  under  heat,  and  in  this  manner  sheets 
of  any  reasonable  dimensions  can  be  obtained,  the  size 
of  which  is  not  restricted  by  that  of  the  natural  pieces. 

Such  built  up  mica  can  be  molded  into  simple  shapes 
of  uninterrupted  flat  or  curved  surfaces  and  has  been 
extensively  employed  in  this  manner  during  the  last  ten 
vears. 


RAW   MATERIALS  25 

Finely  reduced  mica,  the  pulverized  refuse  of  the 
foregoing  and  other  mica  manufacturing  processes,  are 
also  used  in  the  manufacture  of  molded  electrical  insu- 
lation. As  a  filler,  such  compositions,  despite  their  many 
valuable  characteristics,  are  inferior  to  asbestos  fibre. 
Owing  to  its  poor  adhesive  qualities  and  its  chemical  and 
physical  inertness,  mica  adds  no  strength  to  such  mix- 
tures but  rather  weakens  them.  Its  use  as  a  filler,  there- 
fore, is  practically  confined  to  that  type  of  insulators 
under  Class  "A"  in  which  great  dielectric  strength  is 
demanded,  and  for  this  purpose  it  is  far  better  than  any 
other  filler  which  might  be  used. 

Among  the  organic  materials,  shellac  adheres  most 
strongly  to  mica,  and,  therefore,  forms  the  best  binder 
for  mica  insulation. 

SILICA  AND  ITS  COMPOUNDS 

The  element  Silicon — Si — in  combination  with  two 
atoms  of  oxygen,  forming  the  compound  SiO2,  is  generally 
known  under  the  term  of  Silica. 

Silicon  itself  does  not  occur  in  the  free  state  on 
account  of  its  great  tendency  to  combine  with  other  ele- 
ments; but  it  is  found  in  abundance  in  a  great  many  of 
its  compounds,  which  are  of  greater  importance  in  con- 
nection with  molded  electrical  insulation  than  any  other 
organic  or  inorganic  ingredient  employed. 

This  is  due  chiefly  to  the  higher  heat-resisting  prop- 
erties and  chemical  inertness  of  silica.  The  hydrosilicate 
of  alumina — A1203,  2Si02,  2H20 — is  used  in  the  manufac- 
ture of  hydraulic  cements  and  porcelain.  In  the  manu- 
facture of  the  latter,  silica  in  its  various  forms,  such  as 
feldspar,  quartz,  flint,  and  sand,  serves  as  an  opening, 
refractory,  or  as  a  flux  material. 


26  MOLDED    INSULATION 

The  element  silicon,  or  rather  its  compound  Si02, 
occurs  as  chief  constituent  in  a  further  variety  of  forms, 
such  as  kieselguhr,  asbestos,  mica  and  talc,  all  used  in  the 
manufacture  of  electrical  insulation. 

Silica  combines  readily  at  low  temperatures  with 
sodium  or  potassium  hydrates  to  form  silicates  according 
to  the  formula : 

4  Na  OH+Si02=Na4  Si  04+2H2O,  of  which  resulting 
compounds  the  sodium  silicate  is  of  importance. 

This  soluble  silicate,  generally  known  as  waterglass, 
owing  to  its  adhesive  properties,  is  much  employed  in 
the  electrical  art  as  a  fireproof  coating  and  it  has  been 
subject  to  considerable  investigation  and  experimenting 
for  its  use  as  an  inorganic  binder  without  attaining,  how- 
ever, any  success  in  this  direction. 


HYDRAULIC  CEMENT 

The  term  hydraulic  cement  is  used  to  define  that  class 
of  cements  -which  will  harden  under  water. 

This  product  plays  an  important  part  in  the  manu- 
facture of  Molded  Electrical  Insulation  because  of  its 
characteristics  as  a  fireproof  binder  of  materials  of  Class 
"C, "  now  so  widely  used  in  the  electrical  field. 

The  essential  ingredients  of  all  hydraulic  cements 
are  silica,  alumina,  iron  oxide,  and  lime.  In  addition 
to  these,  magnesia  and  other  impurities  are  usually 
present,  together  with  substances  added  to  control  the 
time  of  set.  Of  these  latter,  calcium  sulphate  is  almost 
universally  used. 

Hydraulic  cements  are  so  old  that  history  fails  to 
reveal  their  first  use.  Many  of  the  ancient  races  made 
hydraulic  cement  by  mixing  together  slaked  lime  and 


RAW    MATERIALS  27 

materials  known  as  "PUZZOLANS."  These  "PUZZO- 
LANS"  consisted  of  silica,  alumina,  and  oxide  of  iron, 
and  were  usually  of  volcanic  origin.  Great  care  was 
exercised  by  the  ancients  in  preparing  these  cements. 
They  were  usually  mixed  some  months  before  use,  and 
were  kept  in  cool,  moist  vats,  and  at  intervals  were 
thoroughly  beaten  with  wooden  staves  in  the  hands  of 
slaves.  In  the  use  of  these  cements  in  ancient  times  the 
workmanship  was  of  the  highest  character,  and  in  those 
days  tribes  only,  who  were  successful  in  warfare,  became 
so  opulent  as  to  use  cement.  Such  tribes  necessarily 
had  plenty  of  slaves  as  one  of  the  spoils  of  war,  hence 
labor  was  a  practically  negligible  cost.  As  a  result,  these 
people  working  with  hydraulic  cements  produced  results 
which  we  to-day  are  unable  to  duplicate.  The  explana- 
tion of  this  is  probably  to  be  found  in  the  care  in  prepara- 
tion, and  in  the  skilled  and  thorough  workmanship  in 
the  use  of  cements. 

For  many  centuries  there  was  little  improvement  in 
the  manufacture  of  hydraulic  cements.  However,  in  the 
early  part  of  the  last  -century,  during  the  construction 
of  canals  in  New  York  State,  one  of  the  contractors  dis- 
covered that  by  calcining  and  pulverizing  certain  rock, 
a  very  useful  hydraulic  cement  was  made.  A  plant  was 
established  and  great  quantities  of  this  cement  were 
used  in  the  construction  of  these  canals.  This  cement 
was  given  the  name  of  "ROSENDALE,"  for  the  district 
of  New  York  State  in  which  it  was  first  manufactured. 
In  composition,  the  rock  entering  the  "ROSENDALE" 
Cement  was  a  limestone  carrying  from  ten  to  fifteen 
percent  of  clay  matter. 

The  temperature  of  calcination  was  carried  only  high 
enough  to  expel  the  carbon  dioxide  from  the  calcium  and 
magnesium  carbonates  present  in  this  rock.  No  attempt 


28  MOLDED    INSULATION 

was  made  to  fuse  or  vitrify  the  cement ;  indeed,  if 
partial  or  complete  vitrification  resulted,  the  product 
was  found  to  be  inferior  in  quality.  Somewhat  later, 
rock  of  this  kind  was  discovered  in  the  Lehigh  Dis- 
trict of  Pennsylvania,  and  in  Southern  Indiana,  in  Illinois, 
and  near  Buffalo,  N.  Y.  Thriving  cement  plants 
sprang  up  in  these  regions.  The  class  name  of  i  t  NAT- 
URAL" Cements  was  given  to  these  products,  owing 
to  the  fact  that  they  were  manufactured  from  natural 
rock,  without  addition  of  any  kind.  Their  use  grew 
to  large  proportions,  until  during  the  nineties  several 
million  barrels  per  year  were  manufactured. 

In  1824  Joseph  Aspdin,  an  Englishman,  took  out  a 
patent  covering  the  manufacture  of  a  cement  by  the 
calcination'  of  a  mixture  of  clay  and  limestone.  He 
called  the  resulting  product  "PORTLAND"  Cement, 
owing  to  a  slight  or  fancied  resemblance  to  the  famous 
limestone  quarried  at  Portland,  England,  and  known  to 
all  English  architects  and  contractors  as  "PORTLAND 
STONE." 

The  work  of  Aspdin  was  necessarily  of  a  rudimentary 
nature,  and  little  attempt  was  made  to  closely  control 
the  proportions  of  clay  and  limestone.  Other  investiga- 
tors, however,  continued  his  work,  and  Portland  Cement 
developed  with  rapidity.  In  distinction  to  Natural 
Cement,  it  was  manufactured  from  a  mixture  of  two 
materials,  and  was  calcined  at  a  sufficiently  high  tem- 
perature to  bring  about  vitrification. 

In  earlier  days,  the  raw  materials  were  ground  in  the 
form  of  a  sort  of  mud,  molded  into  bricks,  which  were 
dried  and  burned  in  upright  kilns,  and  these  kilns  were 
charged  with  alternate  layers  of  the  bricks  of  raw  mix 
and  coal.  When  drawn  from  the  kiln,  the  product  had 
to  be  carefully  sorted,  and  was  then  ground  to  a  more 


RAW   MATERIALS  29 

or  less  fine  powder.  Extensive  research  showed  that 
best  results  were  obtained  when  the  finished  cement  con- 
tained from  20  to  23  percent  of  silica,  5  to  8  percent 
of  alumina,  1  to  5  percent  of  iron  oxide,  and  from  60 
to  64  percent  of  lime.  Chemical  control  was,  therefore, 
installed  in  the  Portland  Cement  mills  to  analyze  the  raw 
materials ,  and  so  proportion  them  as  to  bring  this  com- 
position into  the  product.  Methods  of  burning  under- 
went great  development,  and  the  rotary  kiln  utilizing 
powdered  coal  came  into  use,  which  resulted  in  great 
economy.  Further  refinements  were  made  in  the  grind- 
ing machinery. 

With  the  improvement  of  Portland  Cement,  it  was 
found  to  be  superior  in  many  ways  to  Natural  Cement, 
and,  as  the  cost  of  production  of  Portland  Cement  de- 
creased and  energetic  competition  grew  up,  the  price 
fell  gradually,  until,  through  the  combination  of  the 
low  price  and  better  quality,  Portland  Cement  made  seri- 
ous inroads  on  Natural  Cement,  so  that  today  the  produc- 
tion of  the  Natural  Cement  has  fallen  to  an  insignificant 
figure,  while  in  1912  there  were  produced  in  the  United 
States  90,000,000  barrels  of  Portland  Cement. 

A  great  variety  of  raw  materials  is  used  in  the 
manufacture  of  Portland  Cement,  the  essential  being 
that  they  contain  silica,  alumina,  iron  oxide,  and  lime  in 
suitable,  proportions.  A  large  share  of  the  American 
production  of  Portland  Cement  is  made  in  the  Lehigh 
Valley  of  Pennsylvania,  from  material,  called  "Cement 
Rock."  This  rock  contains  the  above  mentioned  in- 
gredients in  such  proportions  that  it  is  in  many  cases 
used  without  the  addition  of  any  other  material.  In 
other  sections  of  the  country,  clay  and  limestone,  shale 
and  limestone,  marl  and  clay,  and  marl  and  shale, 
are  used.  Within  the  past  few  years  large  quantities  of 


30  MOLDED    INSULATION 

Portland   Cement   have   been   manufactured   using   blast 
furnace  slag  and  limestone  as  the  raw  materials. 


ALKALINE  EARTHS 

The  alkaline  earths  to  be  considered  in  connection 
with  molded  insulation  are  lime  and  magnesia. 

In  the  manufacture  of  porcelain,  the  presence  of 
these  ingredients  is  necessary  on  account  of  their  fluxing 
action.  They  are  sometimes  added  in  the  form  of  chalk, 
which  is  simply  a  double  carbonate  of  lime  and  magnesia, 
and  sometimes  in  the  form  of  feldspar. 

Lime  and  magnesia  are  of  equal  importance  in  con- 
nection with  the  inorganic  materials  of  Class  "C."  Con- 
sidering hydraulic  cements,  lime  is  an  essential  ingredient 
of  all  cements  that  have  been  successfully  used  as  binders 
in  Class  "C."  For  this  purpose,  the  lime  is  usually  sup- 
plied by  limestone  or  marl  used  in  connection  with  clay, 
shale,  or  other  silicious  and  aluminous  material.  The 
physical  characteristics  of  the  ingredients  are  of  little 
importance,  since  the  burning  in  the  rotary  kiln  brings 
about  a  complete  metamorphosis  of  the  materials. 

Lime  is  also  present  in  practically  all  inorganic 
binders  other  than  hydraulic  cements.  The  action  of 
these  binders  is  dependent  upon  calcium  silicates  and 
aluminates,  formed  by  proper  combination  of  the  acid 
and  basic  components. 

Magnesia  has  figured  prominently  in  a  type  of  in- 
organic binders  which  more  recently  have  attracted  the 
attention  of  users  of  inorganic  cold  molded  insulation. 

In  1853,  the  Chemist  Sorel  made  the  discovery  that 
zinc  oxide,  when  properly  compounded  with  a  solution  of 
zinc  chloride,  united  with  it,  forming  a  very  hard  cement. 


RAW   MATERIALS  31 

A  little  later  it  was  discovered  that  a  mixture  of  mag- 
nesium chloride  and  magnesia  also  formed  a  strong 
cement.  Chlorides  and  oxides  of  certain  other  elements 
possess  the  same  property,  but  this  has  been  commercially 
utilized  practically  only  in  the  cases  of  the  zinc  and 
magnesium  compounds.  The  setting  of  these  cements 
is  due  to  an  oxychloride.  Such  cements,  comprising 
zinc  oxychloride,  have  found  considerable  application 
in  dental  work.  The  most  important  cement  of  this  class, 
however,  is  that  containing  magnesium  oxychloride,  and 
this  has  found  important  technical  uses. 

It  is  made  by  mixing  calcined  magnesia  writh  a  solu- 
tion of  magnesium  chloride  of  a  density  of  25  to  30 
degrees  Baume.  When  properly  made,  this  cement  is 
superior  in  strength  to  Portland  cement,  but  may  have 
certain  draw-backs,  due  to  improper  methods  of  prepara- 
tion, for  example;  if  the  magnesia  contain  a  small 
quantity  of  residual  carbon  dioxide,  the  cement,  although 
attaining  great  strength,  is  apt  to  crack  badly  during 
setting;  if  the  magnesium  chloride  contain  sulphuric 
acid,  as  is  frequently  the  case,  the  durability  and  ap- 
pearance of  the  cement  are  very  much  injured. 

The  principal  defect  of  such  cements,  however,  as 
they  ordinarily  are  manufactured,  is  that  they  are  not  as 
proof  against  climatic  action  as  the  hydraulic  cements. 

These  cements  are  used  as  binders  in  the  manufacture 
of  emery  wheels,  artificial  stone,  marble,  billiard  balls, 
etc.,  the  fillers  employed  usually  being  of  inorganic 
nature.  As  binders  for  patent  floorings  and  certain  sorts 
of  proprietary  plasters,  such  magnesia  cements  are  in- 
corporated with  asbestos,  flint,  marble-dust,  wood  pulp, 
sawdust,  and  a  great  many  other  organic  or  inorganic 
fillers.  Such  compositions  have  found  a  more  or  less 
commercial  application. 


32  MOLDED    INSULATION 

.      VEGETABLE  FIBRES 

The  vegetable  fibres  most  frequently  employed  in 
the  manufacture  of  molded  electrical  insulation  are  wood 
pulp  and  cotton,  and  to  a  lesser  degree,  hemp,  flax,  and 
straw.  They  are  employed  for  the  same  purpose  as  the 
mineral  fibre,  asbestos,  namely;  to  impart  strength  and 
flexibility  to  the  material. 

Vegetable  fibre,  when  used  in  the  manufacture  of 
the  organic  hot  molded — Class  "A" — the  organic  cold 
molded— Class  "B"— The  Rubber— Class  "E"— and  the 
phenol-formaldehyde— Class  "G" — materials,  is  chemi- 
cally inert  and  performs  merely  a  physical  function  in 
adding  mechanical  strength  and  toughness  to  a  merely 
mechanical  mixture. 

During  the  past  ten  years  vegetable  fibres  have  been 
extensively  employed  by  makers  of  molded  insulation  of 
Classes  "A,"  "B;"  "E"  and  "G,"  because  of  the  fol- 
lowing manufacturing  advantages  which  they  possess. 
They  impart  a  fair  degree  of  mechanical  strength  and 
owing  to  the  fine  structure  of  these  fibres,  they  are  more 
easily  compounded  and  molded  than  mineral  fibre  and 
consequently  the  product  comes  from  the  dies  with  a  finer 
and  more  finished  appearance. 

Another  desirable  quality  is  that,  being  of  a  soft 
nature,  materials  in  which  they  are  employed,  have  a  very 
much  less  abrasive  action  on  the  dies  than  those  employ- 
ing mineral  fibre.  But  as  they  char  at  about  150-deg.  C., 
they  are  unsuited  to  the  manufacture  of  materials  to 
be  subjected  to  any  great  degree  of  heat. 

Furthermore,  their  use  has  been  practically  re- 
stricted to  materials  employing  organic  binders  and  par- 
ticularly to  such  using  the  hot  molding  process. 

Numerous  attempts  have  been  made  to  use  vegetable 


RAW   MATERIALS  33 

fibre  in  conjunction  with  the  inorganic  binders  such  as 
the  silicate  or  other  compounds  of  lime  and  magnesia, 
but  with  indifferent  success  for  electrical  insulating  pur- 
poses, for  while  these  inorganic  substances  partly  combine 
with  the  mineral  fillers  and  make  good  binders,  they  do 
not  combine  with  the  organic  fillers  and  their  binding 
value  when  used  with  these  fillers  is  small,  just  as  when 
sawdust  is  employed  instead  of  sand  to  make  mortar 
with  hydraulic  cement  the  sawdust  does  not  bond  with 
the  cement  and  the  resulting  mortar  is  much  less  strong 
than  when  sand  is  employed. 

As  an  exception,  the  magnesia  chloride  cements 
should  be  mentioned,  which  are  extensively  used  as 
binders  for  vegetable  fibre,  but  such  compounds  have  not 
been  employed  to  any  extent  for  electrical  insulating  pur- 
poses and  for  such  purposes  vegetable  fibre  is  used  only 
in  connection  with  the  natural  organic  or  resinous  binders 
molded  under  heat. 

In  case  of  the  materials  of  cellulose  nature  and  the 
sheet  materials — Class  "H" — however,  the  vegetable  fibre 
plays  a  more  active  part.  In  the  former  it  is  employed 
for  its  basic  chemical  principle  as  cellulose,  while  in  the 
latter  it  is  employed  for  its  physical  structure,  the  other 
ingredients  being  employed  solely  for  their  chemical  or 
physical  action  upon  it. 

The  proper  choice  of  the  vegetable  fibre  in  materials 
of  Classes  "F"  and  "II"  is  of  the  first  importance  as 
in  these  materials  it  undergoes  definite  chemical  or 
physical  changes  which  take  place  under  most  delicate 
conditions. 

CAMPHOR 

Common  or  Japan  Camphor,  as  a  natural  product, 
is  chiefly  produced  in  China,  Japan  and  on  the  Island  of 


34  MOLDED    INSULATION 

Formosa.  The  roots,  branches,  and  trunk  of  the  tree, 
Laurus  Camphora,  are  cut  into  small  pieces  and  subjected 
to  distillation  with  steam.  The  camphor  floats  as  a  white 
solid,  crystalline  mass  upon  the  surface  of  the  watery 
distillation.  The  older  the  trees  are  the  better  will  be 
the  yield  and,  as  a  rule,  only  trees  over  two  hundred 
years  old  are  used.  These  yield  about  three  per  cent, 
of  raw  camphor. 

The  raw  product  contains  an  oil  from  which  the 
camphor  is  separated  by  pressing.  This  oil,  if  subjected 
to  steam  distillation  until  about  two-thirds  of  it  has 
distilled  over,  will  yield  more  camphor,  which  will  settle 
in  the  residue. 

The  raw  camphor  is  then  purified  by  mixing  it  with 
charcoal,  lime,  and  alumina  and  this  mixture  subjected 
to  sublimation  in  glass  retorts. 

Camphor  crystallized  in  the  hexagonal  system  is 
pure  white  in  appearance  and  of  a  strong  aromatic 
odor.  Ordinary  camphor  is  dextro-rotatory.  The  melt- 
ing point  is  175°  C.,  its  boiling  point  204°  C.  and 
its  specific  gravity  .992  at  10-deg.  C.  Camphor  is  very 
volatile  and  sublimes  at  ordinary  temperature.  It  is 
soluble  in  almost  all  organic  solvents.  Small  pieces  of 
camphor  put  upon  water  show  a  very  lively  rotation, 
which,  however,  will  cease  when  traces  of  an  oil  or  a  fatty 
substance  is  poured  upon  the  watery  surface. 

Camphor,  by  reason  of  its  crystaline  character,  its 
extraordinary  reactivity,  its  association  with  the  ter- 
penes,  and  its  comparative  abundance  in  nature,  has 
attracted  the  attention  of  more  than  one  generation  of 
chemists,  and  it  is,  therefore,  one  of  the  oldest  known 
organic  compounds. 

As  early  as  1785  its  effect  on  nitric  acid  was 
known.  Camphor  has  the  formula  C10H160.  However, 


RAW   MATERIALS  35 

no  less  than  thirty  different  formulae  for  camphor  have 
been  proposed  by  different  skillful  chemists  during  the 
last  quarter  of  a  century,  of  which  that  of  Bredt  so  far 
has  received  the  best  confirmation  in  the  discovery  of 
Komppass  Synthesis  of  camphoric  acid. 

Camphor,  synthetically  made,  is  identical  with  the 
natural  product  in  its  form  of  crystallization,  in  its  melt- 
ing point,  solubility,  etc.j  but  is  levorotatory. 

,  Camphor  plays  a  very  important  part  in  the  nitro- 
cellulose industry,  as  it  will  form  with  pyroxylin  or  nitro- 
cellulose a  so-called  solid  solution  generally  known  as 
celluloid,  a  plastic  of  remarkable  flexibility  and  elasticity. 
Although  numerous  attempts  have  been  made  in  the 
celluloid  manufacturing  processes  to  replace  camphor 
with  cheaper  substances,  none  has  been  successfully  ap- 
plied as  yet. 


WOOD   PULP 

This  product  is  obtained  by  disintegrating  wood. 
The  wood  fibres  are  separated  either  mechanically  or 
chemically. 

The  first  variety  is  prepared  by  grinding  the  wood 
under  water,  and  is  of  inferior  quality,  as  the  fibres  are 
short.  The  superior  grades  are  prepared  by  chemical 
means.  The  wood  is  cut  up  and  boiled  under  pressure 
with  a  solution  of  caustic  soda,  sodium  sulphide  or.  best 
of  all,  calcium  bisulphite,  and  the  resulting  soft  product 
is  pulped,  pressed,  and  washed. 

A  special  grade  of  wood  pulp  is  used  as  an  initial 
celluloid  product  in  the  manufacture  of  certain  low  priced 
celluloids. 

It  is  used  extensively  as  a  filler  in  such  hot  molded 


36  MOLDED   INSULATION 

materials  as  Class  "A"  and  in  the  Phenol-Formaldehyde 
products  of  Class  "G-." 

It  is  the  raw  product  in  the  manufacture  of  vulcan- 
ized fibre  and  other  fibrous  insulating  products  described 
in  Class  "H." 


COTTON 

Is  a  plant  of  the  genus  gossypium.  It  is  one  of  the 
most  important  vegetable  fibres,  and  on  account  of  its 
characteristic  spiral  thickening  is  readily  distinguished 
from  all  others  and  is  especially  adaptable  to  spinning. 

At  least  fifty  species  of  Gossypium  are  known,  nearly 
all  of  which  produce  lint  upon  their  seeds,  but  very  few 
enter  into  consideration  in  the  production  of  the  com- 
mercial crop. 

The  Upland  cottons  of  the  United  States  are  variously 
referred  to  as  Gossypium  Herbaceum  and  Gossypium 
Hirsutum. 

In  this  country  two  distinct  types  of  cotton  are 
recognized.  The  Sea  Island,  with  its  small,  smooth,  black, 
seeds  and  long,  fine  lint,  and  the  Upland  type  with  a 
greenish  seed,  shorter  lint,  and  a  closely  adherent  fuzz 
about  the  seed,  known  as  linters.  The  Sea  Island  Cotton 
is  grown  to  greatest  perfection  on  the  islands  and  low- 
lying  coast  of  South  Carolina,  Georgia  and  Florida;  also 
in  the  West  Indies  and  in  Egypt. 

The  fibre,  when  well-grown,  measures  1.5"  to  2"  in 
length,  and  being  very  fine,  is  in  constant  demand  for  the 
finer  numbers  of  threads  and  yarns,  for  which  it  com- 
mands a  high  price. 

The  Upland  cotton  is  grown  over  a  wide  area  of  the 
United  States  and  furnishes  by  far  the  greater  portion 


RAW   MATERIALS  37 

of  the  crop.  It  is  cultivated  throughout  the  region  from 
Virginia  to  Oklahoma,  and  southward. 

The  fibre  of  this  type  is  usually  shorter  and  coarser 
than  that  of  the  Sea  Island,  but  by  careful  crossing  and 
selection,  varieties  are  being  secured  that  approach  the 
lower  grades  of  Sea  Island  in  quality. 

Cotton  is  an  initial  raw  material  in  the  manufacture 
of  celluloid  and  its  treatment  for  such  is  described  under 
the  chapter  devoted  to  that  material. 

It  is  also  employed  as  a  fibrous  filler  in  the  manu- 
facture of  the  hot  molded  materials  of  Class  "A." 

From  it,  the  better  qualities  of  the  vulcanized  fibre 
or  other  paper  insulating  products  are  made,  but  owing 
to  its  high  cost,  it  is  not  used  to  any  great  extent  for 
such  purposes. 


HEMP 


Cannabis  Sativa  is  an  erect  growing  plant  originat- 
ing in  Asia.  It  resembles  very  much  in  its  general  ap- 
pearance the  common  stinging  nettle.  Both  belong  to 
the  same  family — Urticaceae. 

Its  cultivation  is  similar  to  that  of  flax.  The  young 
plants  are  thinned  out  when  they  are  three  or  four 
inches  high,  and  are  left  from  eight  to  twelve  inches 
apart.  If  intended 'for  fibre  alone,  the  stems  are  all 
pulled  and  treated  alike  and  it  is  principally  for  its 
fibre  that  hemp  is  cultivated.  This  is  obtained  by  rot- 
ting the  stems  of  the  plant,  (on  the  same  principle  as  is 
followed  in  separating  flax  fibre. 

Hemp  is  grown  in  the  Philippine  Islands  arid  Europe. 


38  MOLDED    INSULATION 

FLAX 

Flax  or  Linum  Usitatissimum  belongs  to  the  natural 
order  of  Linaceae  and  is  unknown  in  the  wild  state.  Its 
cultivation  dates  from  pre-historic  times,  bundles  of  un- 
worked  flax  having  been  found  in  the  ancient  lake  dwell- 
ings in  Switzerland. 

The  flax  fibre  is  found  within  the  cortex  of  the  stem 
and  is  easily  separated  after  the  flax  straw  has  been 
rotted  in  water.  This  process  is  followed  by  drying 
and  stacking,  and  afterwards  by  breaking  and  scutching, 
which  completely  separates  the  fibre. 

Flax  is  produced  principally  in  Austria,  Belgium, 
France,  Germany  and  Russia.  It  is  also  grown  in  the 
United  States,  but  in  this  country  it  is  cultivated  almost 
entirely  for  its  seed  and  not  for  its  fibre. 

The  flaxes  are  herbaceous  or  sub-shrubbery  plants, 
their  stems  being  remarkably  tough. 

New  Zealand  flax  is  a  liliaceous  plant  and  also  yields 
a  valuable  fibre,  which  is  stripped  by  machinery  and 
used  for  making  baskets,  ropes,  etc. 

Flax  is  comparatively  of  little  importance  in  con- 
nection with  the  manufacture  of  electrical  molded  in- 
sulation. 

ASPHALTS 

The  term  "asphalt"  is  applied  to  a  series  ,of  bit- 
uminous substances  generally  black  in  color,  which  are 
hard  at  ordinary  temperatures,  become  viscous  at  about 
70-deg.  C.,  and  melt  at  about  100-deg.  C.  Their  specific 
gravity  varies  from  1.04  to  1.40.  Chemically,  they  are 
compounds  of  carbon  and  hydrogen  and  their  sulphur 
and  nitrogen  derivatives. 


RAW   MATERIALS  39 

They  may  be  divided  into  two  groups;  the  "NAT- 
URAL "'and  the  "ARTIFICIAL." 

Natural  asphalts  occur  in  various  parts  of  the  world, 
notably  in  United  States,  Trinidad,  Barbadoes,  Venezuela, 
Mexico,  Cuba,  Egypt,  Russia,  and  India.  They  are  found 
as  mineral  deposits  embedded  in  the  earth,  sometimes 
containing  lime  and  other  impurities,  or  in  the  so-called 
asphalt  lakes,  such  as  those  in  Trinidad  and  Venezuela. 

The  asphalts  in  which  we  are  particularly  interested 
are  the  mineral  asphalts  of  Utah,  Colorado  (Gilsonite) 
and  Barbadoes  (Manjak),  which  are  peculiarly  free  from 
impurities  and  are  the  ones  generally  employed  in  the 
manufacture  of  electrical  insulation. 

The  "ARTIFICIAL"  asphalts  are  prepared  by  the 
distillation  of  asphaltic  petroleum,  resemble  the  softer 
natural  asphalts  in  some  respects  and  are  often  marketed 
as  such,  especially  when  prepared  for  some  specific 
purpose. 

In  addition  to  the  natural  and  artificial  asphalts, 
coal-tar  residues  or  pitch,  derived  from  the  distillation  of 
coal  tar,  are  extensively  used  for  many  similar  purposes. 
Coal-tar  pitch  differs  materially  in  chemical  composition 
from  the  natural  bitumens.  It  is  more  brittle  than  the 
hard  asphalts,  but  melts  more  readily  and  is  more  fluid  un- 
der heat.  The  artificial  asphalts  and  coal-tar  pitch  are 
both  extensively  used  in  the  manufacture  of  electrical  in- 
sulation and  for  this  purpose  are  about  as  equally  valu- 
able as  the  natural  asphalts. 

Stearine  Pitch,  obtained  as  a  by-product  in  the  treat- 
ment of  vegetable  and  animal  oils  and  fats  for  the  produc- 
tion of  stearic  acid,  is  much  softer  than  those  mentioned 
above  and  is  of  great  value  in  insulating  compounds, 
because  of  its  ability  to  stand  very  high  temperatures 
without  drying  out  and  becoming  brittle,  and  is  employed 


40  MOLDED   INSULATION 

in  the  manufacture  of  insulating  varnishes,  cloths,  and 
tapes,  as  well  as  in  binders  for  the  manufacture  of  molded 
insulating  parts. 

Ozokerite,  a  solid  bitumen,  consisting  largely  of  par- 
affine  hydro-carbons,  and  ceresin  wax  prepared  therefrom, 
are  important  raw  materials  used  for  insulating  pur- 
poses. "CERESIN"  Wax  melts  between  60-deg.  C.  and 
70-deg.  C.,  and  owing  to  the  fact  that  it  then  becomes 
a  very  limpid  fluid,  it  has  much  higher  saturating  quali- 
ties and  is  a  far  better  impregnating  material  for  tapes, 
clothes,  and  molded  insulating  pieces  than  the  heavier 
and  more  viscous  asphalts  or  pitches. 

Pitch  obtained  from  the  distillation  of  wood  and 
brown  coal  is  also  used  to  some  extent,  but  due  to  its 
very  brittle  nature  is  of  comparatively  little  value. 

It  is  self-evident  that  the  harder  the  asphalt,  that 
is  the  higher  its  melting  point,  the  greater  will  be  its 
heat-resisting  properties,  but  unfortunately,  the  brittle- 
ness  increases  with  the  hardness. 

The  chemical  and  physical  characteristics  of  some 
asphalts  are  such  that  they  are  well  suited  for  use  in 
compounding  with  rubber,  and  for  this  purpose  are  ex- 
tensively and  successfully  employed. 

Pure  asphalts  and ,  mineral  pitches  are  unaffected 
physically  or  chemically  by  water,  acids,  or  alkalies  and 
this  inert  characteristic  coupled  with  their  high  di-elec- 
tric  strength,  their  low  cost.,  and  the  facility  with  which 
they  can  be  manipulated,  renders  .them  of  the  greatest 
importance  in  the  manufacture  of  electrical  insulating 
materials.  >•!»..••'.-• 

.They  have  a  considerable  advantage  over  the  copal 
resins  in  that  they  ,dp  not  have  to-.be  distilled  to  render 
Jthem  suitable  for  the  manufacture  of .  varnishes  and  other 
compounds  used  in  the  preparation  of  Binders  ^employed 


RAW   MATERIALS  41 

in  the  manufacture   of  molded  insulation,   as  they  fuse 
or  melt  readily  when  subjected  to  heat. 


SHELLAC 

The  story  of  the  production  of  shellac  is  perhaps 
more  interesting  than  that  of  any  other  material  used  in 
the  manufacture  of  molded  insulation. 

Lac  is  a  vegetable  substance  as  it  is  the  sap  of  a 
tree,  but  it  is  also  an  animal  product  in  that  it  is  exuded 
by  an  insect. 

These  insects  (the  coccus  lacca,  carteria  lacca,  etc.) 
infest  several  species  of  trees  growing  in  India  and 
southern  Asia,  notably  certain  varieties  of  fig  trees. 

The  female  produces  the  lac  to  protect  her  eggs.  This 
insect,  after  attaching  itself  to  the  plant,  remains  fixed 
there  and  proceeds  to  extract  the  resinous  sap  and  to 
convert  it  into  lac,  with  which  she  incrusts  herself  and 
in  which  she  deposits  her  eggs. 

In  a  short  time,  the  eggs  burst  into  life,  and  the 
young,  which  are  very  minute,  eat  their  way  through  the 
dead  bodies  of  their  parents,  and  swarm  all  over  the 
twig  or  small  young  branch  of  the  tree  in  such  countless 
numbers  as  to  .give  it  the  appearance  of  being  covered 
with  a  blood-red,  dust.  ..,,,,.  ,,  ,,,,,. 

:  ,,The  method  of  preparing  the  lac  for  market  is  crude 
but  effective:.  TJie  .incrusted  twigs,  when  broken  from 
the,  trees,  are  known  as  .sticji. lac.  The  brittle  lac  is 
readily  removed  Jrpm  the  sticks  .by  nieans  of  rollers. 

The  crude  lac,  which  ^s,  of  a  <dark  red  cplpr  and  con- 
tains about  .68  ,per  .cenjt,.,  resin,  is  now  placed  into  tubs  of 
\yarm  wa.t.ex,  and  beaten  with  pestles  or  trodden  by  men.  By 


42  MOLDED    INSULATION 

this  means  it  is  freed  from  the  bodies  of  the  insects, 
the  dirt,  vegetable  matter,  and  much  of  its  coloring. 

The  lac,  now  termed  seed  lac,  is  removed  from  the 
matter  and  the  latter  boiled  down  and  molded  into  cakes. 
This  product,  known  as  "lac-lake,"  was  very  widely 
used  before  the  introduction  of  coal-tar  colors  as  a  red 
dye  for  textiles,  and  is  still  much  used  in  the  countries 
where  it  is  produced. 

The  seed  lac  is  now  placed  in  cotton  bags  and  held 
before  a  charcoal  fire,  the  melting  lac  being  squeezed 
through  the  cloth  by  twisting  the  bag.  It  is  now  ladled 
from  the  trough  into  which  it  has  dropped  and  poured 
over  and  spread  upon  a  slowly  revolving  roller  upon 
which  it  soon  sets  and  hardens,  when  the  thin  shell 
of  lac  is  cut  or  scraped  from  the  roller  with  a  knife, 
and  the  shell  lac  or  shellac  is  ready  for  market. 

The  best  of  the  shellac  made  in  this  way  is  of  a 
light  brown  color,  nearly  transparent,  and  is  known  as 
"orange  shellac." 

The  lower  grades,  not  so  free  from  coloring  matter 
and  foreign  substances,  are  usually  molded  into  thin 
sheets  or  discs  and  sold  under  the  names  of  button  lac, 
garnet  lac,  etc. 

It  is  chiefly  used  as  a  binder  for  materials  of  Class 
"A."  It  melts  more  perfectly  than  asphalt  or  other 
natural  resinous  bodies,  with  the  exception  of  rosin,  al- 
though its  melting  point  is  higher  than  these  adulterants. 

It  is  impervious  to  water  and  stable  under  ordinary 
climatic  conditions.  It  forms  a  very  tough  binder  and 
is  superior  in  this  respect  to  asphalts,  pitches,  and  resins, 
but  unfortunately  much  liable  to  adulteration  with  the 
latter,  owing  to  its  higher  price. 

Shellac  is  also  used  as  a  binder  for  mica  and  its 
binding  qualities  for  this  material  are  superior  to  any 


RAW    MATERIALS  43 

other  kind  known  to-day. 

It  is  used  extensively  in  solution  in  alcohol  as  a  quick 
drying  insulating  varnish. 

It  is,  or  ought  to  be,  the  principal  ingredient  in  the 
manufacture  of  insulating  sealing  waxes,  used  for  sealing 
up  metal  parts  in  assembled  porcelain  insulators,  but  un- 
fortunately, as  in  the  case  of  molded  insulating  materials 
of  Class  "A,"  it  is  replaced  for  this  purpose  by  cheaper 
resinous  products  such  as  rosins,  asphalts,  etc. 


RESINS 
COPAL 

This  term  is  broadly  applied  to  a  number  of  fossil 
gums.  The  botanical  origin  of  these  resins  is  not  defi- 
nitely known  although  some  of  them,  particularly  those 
of  more  recent  fossil  origin,  can  be  partly  traced  to 
trees,  species  of  which  are  still  extant. 

The  copals  are  found  chiefly  in  East  and  West  Africa, 
New  Zealand,  Java,  South  America  and  the  Philippine 
Islands.  The  older  fossils  are  collected  by  natives  em- 
ploying very  primitive  methods  and  are  gathered  from 
the  beds  of  lakes  and  streams  or  dug  from  the  earth 
during  the  wet  season  by  open  mining  to  a  depth  of 
about  fifteen  feet. 

Copal  is  found  in  the  market  in  many  shapes  and 
varies  greatly  in  color.  In  form  it  ranges  from  small 
pebble  like  particles  to  blocks  two  feet  in  diameter.  The 
size  depends  on  the  kind  of  copal.  It  is  also  found  as 
chips,  slabs,  and  angular  lumps  of  irregular  form.  It 
is  usually  of  a  yellowish  or  brownish  amber  color  and 
is  almost  always  covered  with  a  crust  of  variable  color. 


44  MOLDED    INSULATION 

which  must  be  removed  in  water  or  lye  or  by  mechanical 
means,  the  latter  method  being  preferable. 

In  quality  copals  are  graded  according  to  the  fol- 
lowing characteristics : 

Hardness  or  toughness. 

Color. 

Solubility  and  melting  point. 

The  harder  copals,  Zanzibar,  Mozambique,  Sierre 
Leone,  Angola,  Benguella,  Gabon,  are  usually  the  higher 
priced.  Among  the  softer  copals  are  the  Manilla  and  the 
Kauri. 

The  melting  point  of  copals  varies  from  75-deg.  C. 
to  450-deg.  C.,  the  harder  having  the  higher  melting 
points. 

The  solubility  of  copal  has  been  the  subject  of  much 
analytical  research  and  while  many  of  these  gums  are 
more  or  less  soluble  in  alcohol,  ether,  benzol,  benzine, 
acetone,  turpentine,  chloroform  and  carbon  disulfide,  in 
manufacturing  it  is  practical  to  dissolve  them  only  after 
they  have  been  melted.  This  process  is  briefly  as  follows : 
the  copal,  after  having  been  cjeaned,  is  sorted  according 
to  color  and  size  and  the  larger  pieces  crushed  or  ground. 
It  is  then  heated  to  get  rid  of  such  water  as  may  be 
present  and  then  melted  over  an  open  ffre  or  subjected 
to  a  process  of  destructive  distillation  to  drive  off  the 
resinous  oils.  The  loss  from  this  operation  varies  from 
10%  to  40%  by  weight.  The,  process  is  one  requiring 
great  care  and  experience,  for  the  point  at  which  the 
malting  or  distillation  is  arrested  plays  a  most  important 
part  in  the  value  of  the  product.  This  point  is  determined 
by  collecting  and  watching  the  amount  of  resin-oil  dis- 
tilled over  or  by  .carefujly  watching  the,  appearance, 
temperature,  and  condition  of  the  melted  resin  and  de- 


RAW   MATERIALS  45 

pending  upon  the  skill  and  experience  of  the  operator, 
the  latter  method  usually  giving  the  better  results. 

If  the  heating  is  carried  too  far  and  too  much  oil 
is  driven  off,  not  only  is  the  loss  in  weight  unnecessarily 
great,  but  the  copal  loses  some  of  its  toughness  and  other 
desirable  qualities.  The  interruption  of  the  distilling 
process  at  the  proper  moment  is,  therefore,  of  prime 
importance. 

After  being  subjected  to  the  distilling  process,  as 
described  above,  the  copal  gums  are  soluble  in  various 
oils  and  other  solvents,  and  in  such  form  are  of  the 
highest  importance  in  the  electrical  art,  not  only  in 
the  field  of  molded  insulation,  but  to  an  even  greater 
extent  for  a  wide  range  of  uses  in  the  preparation  of 
insulating  varnishes,  impregnating  compounds,  insulating 
cloths,  and  the  like.  Copals  and  copal  preparations,  when 
properly  prepared,  are  unaffected  by  climatic  influences, 
especially  those  of  the  earlier  fossil  origin,  and  in  proper 
combination  with  suitable  solvents  and  inorganic  ad- 
mixtures possess  great  heat-resisting  and  dielectric  prop- 
erties and  will  withstand  continuously  a  temperature  of 
200-deg.  C.  These  properties  render  copal  one  of  the 
most  important  materials  in  common  use  in  electrical 
manufacture. 

While  the  chemical  nature  of  copals  is  as  yet  unde- 
termined, or  at  least  but  incompletely  determined,  their 
physical  properties  render  them  of  the  utmost  importance 
in  the  electrical  arts. 

,     •    •  ,.•>-:,       ,;        "-..T-:,         :-;•    ••ii'VsW'      ,        i1 

RESINS 
DAMMAR  GUM 

This  variety  of  resin  is  obtained  from  the  amboyna 
pine  and  comes  principally  from  Java  and  Sumatra.  It 


46  MOLDED    INSULATION 

exudes  sap  naturally  like  the  spruce  and  other  members 
of  the  pine  family,  but  this  yield  is  increased  by  making 
incisions  in  excrescences  which  grow  on  the  trunk  of 
the  tree.  It  is  also  gathered  in  considerable  quantities 
from  the  beds  of  streams  flowing  through  the  districts  in 
which  the  tree  is  found.  It  comes  to  the  market  in  small, 
usually  transparent,  homogeneous,  lumps.  Its  principal 
use  in  insulating  manufacture  is  in  binders  for  the  hot 
molded  organic  materials  (Class  "A"). 

It  begins  to  melt  at  80  deg.  C.,  and  at  100-deg.  C. 
it  commences  to  flow  rapidly.  It  does  not  melt  as 
readily  as  rosin,  but  more  readily  than  other  resins  of 
the  copal  series. 

It  is  soluble  in  benzole,  turpentine,  and  ether  with- 
out the  application  of  heat.  It  is  also  soluble  in  benzine, 
in  which  it  differs  from  most  other  resins. 

Although  affected  by  atmospheric  exposure,  it  is 
much  more  stable  under  these  influences  than  rosin  and  is 
much  to  be  preferred  to  it,  and  would  supersede  this 
gum  entirely  were  it  not  for  its  higher  cost. 


ROSIN 

The  term,  rosin,  is  applied  to  the  residue  obtained 
from  the  distillation  of  the  resinous  exudation  of  various 
species  of  the  pine  tree,  the  volatile  portion  which  dis- 
tills over  being  turpentine. 

It  is  found  in  the  market  in  hard,  homogeneous 
masses  and  varies  greatly  in  quality.  The  quality  depends 
upon  the  percentage  of  turpentine  distilled  off  as  well  as 
upon  the  quality  of  the  resinous  exudation  from  which  it 
was  derived.  In  color,  it  varies  from  a  light,  transparent, 


RAW   MATERIALS  47 

yellow  amber  to  almost  black.  It  is  quite  hard  and  very 
brittle  and  softens  readily  under  heat  at  75°  C.,  becoming 
a  thin  liquid  at  about  100°  C.,  above  which  temperature  it 
decomposes. 

It  has  the  property  of  becoming  a  limpid  liquid  at 
comparatively  low  temperatures,  which  makes  it  so  use- 
ful a  substitute  for  shellac  in  the  organic  cold  molded 
materials.  It  is  not  much  used  in  the  manufacture  of 
electrical  insulation,  except  for  this  purpose,  but  finds 
manifold  uses  in  various  of  the  liberal  arts. 

The  use  of  rosin*  in  the  manufacture  of  molded  in- 
sulation should  be  discouraged,  since  its  cheapness  is 
its  only  recommendation.  Many  attempts  have  been 
made  to  render  it  more  heat-proof  and  to  give  it  a  more 
stable  nature,  but  while  much  literature  has  been  pub- 
lished on  this  subject,  very  little  practical  result  has  been 
attained. 


PARAFIN  WAX 


This  term  is  applied  to  a  variety  of  hydrocarbons  of 
the  paraffin  series,  obtained  ffom  shale  oils.  It  is  a  solid 
softening  readily  at  50-deg.  C.,  and  was  formerly  used 
for  impregnating  electrical  insulation  materials. 

But  owing  to  its  low  melting  point  it  is  but  very  little 
used  for  such  purposes  to-day. 

The  reason  it  retains  its  place  among  the  substances 
in  use  for  the  manufacture  of  electrical  insulating  ma- 
terials is  that  it  will  withstand  the  action  of  alkalies  better 
than  any  other  organic  insulating  substance.  It  is  also  un- 
affected by  strong  acids  at  ordinary  temperatures. 


48  MOLDED    INSULATION 

LINSEED  OIL 

This  oil  is  obtained  by  pressing  the  seeds  of  the  flax 
plant.  According  to  the  character  of  the  seeds  and  the 
method  of  extraction  employed,  the  oil  Varies  from  a  pale, 
tasteless,  product  to  'an  amber  or  yellowish  colored, 
limpid,  liquid  of  characteristic  taste. 

It  is  of  incalculable  value  in  the  electrical  arts  and  is 
extensively  employed  in  conjunction  with  resins  and  as- 
phalts for  the  manufacture  of  varnishes  and  impregnating 
compounds.  In  such  preparations, 'it  acts  not  only  as  a 
solvent,  but  due  to  the  fact  that  it  absorbs  oxygen  from 
the  air,  it  has  an  oxydizing  effect  upon  the  resinous  and 
asphaltic  bodies  with  which  it  is  mixed.  This  is  par- 
ticularly true  of  the  boiled  linseed  oil,  which  will  continue 
to  increase  in  weight  by  the  absorption  of  oxygen  from 
the  air  until  it  becomes  viscous  or  even  hard.  In  practice, 
this  drying  or  oxygen  absorbing  property  is  increased 
or  hastened  by  the  addition  of  metallic  oxydizing  agents. 

Linseed  oil  is  used  not  only  in  combination  with  other 
substances,  but  the  boiled  oil  itself,  without  other  ad- 
mixtures, except,  perhaps,  driers,  is  used  to  a  considerable 
extent  for  impregnating  and  coating  clothes  and  tapes 
as  well  as  for  treating  molded  insulation  and  insulating 
parts. 

A  number  of  methods  have  been  proposed  and  con- 
siderable patent  literature  is  available  relating  to  the 
production  of  solid  resinous  products  from  linseed  oil 
which  might  be  substituted  for  shellac  asphalts  or  resins 
in  the  manufacture  of  molded  insulation.  The  object 
of  these  experiments  was  to  take  advantage  of  the  high 
heat-resisting  properties  of  the  resinified  linoxen  pro- 
ducts in  the  manufacture  of  such  materials  as  those  of 
Class  "A'"  (the  organic  hot  molded  materials),  but  no 


RAW    MATERIALS        .  49 

great  success  has  been  attained  in  this  direction,  partly 
owing  to  the  fact  that  one  of  the  chief  advantages  of 
employing  shellac  and  similar  binders  for  materials  of 
this  class  lies  in  their  property  of  becoming  plastic  under 
heat  during  the  molding  process,  and  the  linoxen  products 
are  far  less  plastic  than  shellac  and  consequently  are  not 
so  easily  molded. 

On  the  other  hand,  considerable  success  has  attended 
the  compounding  of  linoxen  products  with  rubber  and  as- 
phalts to  produce  rubber  substitutes  which  are  success- 
fully employed  in  the  manufacture  of  molded  insulation. 

Another  interesting  application  of  linseed  oil  which 
has  been  proposed,  consists  in  heating  cellulous,  starch, 
refuse  horn,  hoof  by-products,  and  other  materials, 
with  linseed  oil  to  a  temperature  beyond  the  point  of 
decomposition,  at  which  temperature  the  components  were 
supposed  to  react  upon  each  other  to  form  a  new  resinous 
substance. 

Unfortunately,  beyond  laboratory  experiment  and 
elaborate  patent  literature,  nothing  noteworthy  was  de- 
veloped. 

Owing  to  its  high  price,  linseed  oil  is  subject  to 
much  adulteration  and  replacement  by  rosin  oil,  mineral 
oils,  and  other  cheaper  oils,  and,  while  it  is  often  difficult 
to  detect  the  presence  of  such  adulterants  analytically, 
their  imperfect  drying  and  poor  elastic  qualities  soon 
proclaim  them  in  practice. 


VARIOUS  OTHER  DRYING  OILS 

Besides  linseed  oils,  there  are  a  few  other  oils  used  in 
connection  with  the  utilization  of  resins  and  asphalts 
for  insulating  purposes. 


50  MOLDED    INSULATION 

Among  such    the  following  are  worthy  of  mention : 

Chinese  wood  oil  or  Tung  oil:  This  oil  is  obtained 
from  the  seeds  of  the  Ying  tzu  tung,  a  tree  indigenous 
to  China,  and  is  used  in  very  considerable  quantities  as 
a  substitute  for  linseed  oil.  This  product  exhibits  one 
marked  difference  from  linseed  oil  in  that  it  dries  at  a 
uniform  rate  throughout  its  mass,  whereas  the  latter 
dries  from  the  surface  inward. 

Soja  bean  oil :  Obtained  from  the  fruit  of  the  Soja 
bean  tree. 

Poppy  seed  oil:  Obtained  from  the  plant  Papaver 
Somniferum. 

Rosin  oil:  Obtained  from  the  dry  distillation  of 
rosin.  This  oil,  owing  to  its  low  price,  is  a  common 
adulterant  of  linseed  oil.  Its  drying  qualities  are  not 
equal  to  those  of  linseed  oil  and  it  is  of  such  an  un- 
stable nature  as  to  make  its  use  inadvisable  for  elec- 
trical insulating  purposes. 


MINERAL  OIL  SOLVENTS 

Various  derivatives  distilled  from  petroleum  and  coal- 
tar  at  different  temperatures  are  employed  in  the  manu- 
facture of  liquid  compounds  of  resins  and  asphalts. 

They  are  usually  cheaper  than  the  drying  oils  and 
do  not  dry,  or  rather  evaporate  readily,  which  is  a  source 
of  frequent  complaint  from  users  of  these  liquid  solutions 
or  compounds. 

They  are  employed  in  the  manufacture  of  impregnat- 
ing compounds  and  cheap  insulating  varnishes,  as  well  as 
for  impregnating  insulating  cloths  and  tapes. 

Their  evaporative  qualities  vary  greatly.  Some  will 
dry  or  evaporate  on  exposure  to  the  atmosphere,  while 


RAW   MATERIALS  51 

others  require  considerable  heat.     This  variation  renders 
them  applicable  to  a  wide  range  of  purposes. 

TURPENTINE 

This  well-known  solvent  is  obtained  from  the  dis- 
tillation of  the  exudations  from  various  species  of  the 
pine  tree.  It  is  the  volatile  product  of  the  distilling  pro- 
cess, the  residue  being  rosin. 

It  is  much  valued  for  its  use  in  connection  with  dis- 
solving waxes,  resins,  and  similar  materials  used  for 
electrical  insulating  purposes. 

When  exposed  to  the  air,  it  dries  slowly  but  steadily 
by  absorbing  oxygen.  The  major  part  of  it  evaporates, 
leaving  a  minor  part  of  resinous  hard  substance  behind. 

In  this  respect  of  drying  by  absorption  of  oxygen, 
turpentines  differ  from  other  solvents,  such  as  naphtha, 
benzol,  etc.,  as  these  latter  solvents  evaporate  rapidly 
and  leave  no  residue  behind. 

BENZINES 

Benzene  obtained  from  the  distillation  of  coal-tar, 
and  the  benzine  or  benzoline  obtained  from  the  distilla- 
tion of  petroleum  oils,  are  both  widely  used  as  quick  vola- 
tile solvents  for  asphalts,  resins,  and  copal  oil  compounds, 
because  of  their  excellent  dissolving  properties  and  vola- 
tile characteristics. 

ALCOHOLS 

Among  the  alcohols  ethyl  or  grain  alcohol  and  methyl 
or  wood  alcohol  are  both  used  to  a  considerable  extent 
for  dissolving  the  resinous  organic  binders  in  the  manu- 
facture of  insulation  products. 


52  MOLDED   INSULATION 

They  are  principally  used  to  dissolve  shellac  and 
other  alcohol  soluble  gums.  Such  solutions  are  also  of 
great  importance  in  the  manufacture  of  built  up  mica 
and  quick  drying  shellac  gum  varnishes. 


CAOUTCHOUC  OR  CRUDE  RUBBER 

This  is  the  name  given  to  the  product  of  the  milky 
latex  which  exudes  from  incisions  made  in  tlie  bark  of 
certain  trees  found  in  tropical  and  semi-tropical  countries. 

While '  many  trees  produce  this  latex  to  a  greater 
or  lesser  degree,  there  are  certain  regions  which,  in  the 
quality  and  quantity  of  this  product,  surpass  all  others. 
At  the  present  time  the  rubber  trees  found  in  the  Amazon 
District  of  South  America  give  a  latex  which  in  purity 
and  quantity  surpasses  any  now  known.  Generally  speak- 
ing the  world's  supply  of  crude  rubber  comes  from 
Central  America.  South  America,  Africa,  and  Asia.  The 
quality  of  the  rubber  is  rated  in  the  order  named. 

While  the  methods  of  handling  are  different  in  the 
various  districts,  the  ultimate  result  is  the  collection  of 
the  milk  or  latex  found  in  the  bark  of  the  trees,  and 
the  reducing  of  it  by  certain  processes  to  the  commodity 
known  as  crude  rubber.  The  latex  consists  of  rubber, 
resins,  and  other  organic  substances,  and  water.  In  the 
Hevea  plant,  which  is  considered  one  of  the  best  of  the 
Amazon  trees,  only  30%  to  32%  of  the  latex  is  rubber. 
In  other  trees  the  percentage  is  even  less.  Crude  Rubber 
contains  more  or  less  foreign  matter  according  to  the 
manner  in  which  it  is  collected. 

In  the  Amazon  District  care  is  taken  to  prevent  the 
latex  from  coming  in  contact  with  alien  matter  with  the 
result  that  the  loss  due  to  this  cause  is  verv  small.  The 


RAW    MATERIALS  53 

African  and  Asiatic  trees  are  carelessly  cut  and  handled, 
often  permitting  the  flowing  latex  to  drip  down  the  sides 
of  the  trees  to  the  ground  with  the  Vesult  that  stones, 
earth,  leaves,  etc.,  are  collected  with  it.  The  loss  from 
such  careless  methods  is  often  as  much  as  sixty  per- 
cent. 

The  consumption  of  rubber  is  steadily  increasing 
and  new  uses  are  being  found  for  it  every  day.  Conse- 
quently the  supply  of  crude  rubber  is  naturally  one  to 
be  looked  to  with  some  concern.  The  likelihood  of  an 
inadequate  supply  before  many  years  and  the  constantly 
increasing  price  of  crude  rubber  has  resulted  in  the  plant- 
ing of  rubber  trees  in  the  districts  where  these  trees  are 
found  in  their  native  state.  The  rubber  obtained  from 
such  cultivated  trees  is  known  as  "PLANTATION"  Rub- 
ber and  is  usually  of  a  higher  grade  than  the  wild  rubber. 

Rubber  in  its  crude  state  is  very  seldom  used  com- 
mercially as  it  is  very  susceptible  to  atmospheric  changes. 
At  a  temperature  of  51.7  deg.  C.  it  becomes  very  sticky 
and  has  great  adhesiveness,  while  at  0  deg.  C.,  it  is 
very  hard  and  brittle  and  is  easily  broken.  To  over- 
come these  faults  the  process  known  as  vulcanization  is 
resorted  to,  the  principle  of  which  is  the  incorporation 
of  sulphur  in  some  form  and  the  subsequent  heating  of 
the  mixture.  The  sulphur  in  general  use  for  vulcaniza- 
tion is  in  the  form  of  flowers  of  sulphur.  This  form  of 
sulphur  has  a  specific  gravity  of  2.00  and  in  good  com- 
mercial form  is  of  a  bright,  lemon  color.  It  is  insoluble 
in  water  and  alcohol  and  mixes  readily  with  crude  rub- 
ber. In  mixing  the  sulphur  with  the  rubber  care  is 
taken  to  thoroughly  incorporate  it  by  running  the  two 
materials  together  through  iron  rollers  which  are  so 
geared  as  to  travel  at  different  speeds,  which  in  so  doing 
not  only  press  the  materials  thoroughly  together,  but 


54  MOLDED   INSULATION 

also  exert  a  pulling  stress  upon  the  mass.  Crude  rubber 
when  properly  mixed  with  sulphur  and  vulcanized  under- 
goes changes  in  both  its  physical  and  chemical  properties. 
It  is  not  then  affected  by  ordinary  changes  of  tempera- 
ture. Its  elasticity  is  greatly  increased,  and  it  is  not 
soluble  to  any  great  extent  in  such  agents  as  naphtha  or 
chloroform,  which,  before  the  admixture,  readily  reduced 
it  to  a  liquid  solution. 

There  are  a  number  of  methods  of  vulcanizing  rub- 
ber, the  principal  one  being  known  as  the  steam  process. 
In  this  process  the  steam  may  come  in  direct  contact 
with  the  mass  held  in  a  large  cylinder  or  tank,  or  the 
heat  of  the  steam  may  be  exerted  on  the  outside  of  a 
mold  which  holds  the  rubber  mass,  this  mass  having  no 
contact  with  the  steam  itself.  Before  being  subjected  to 
the  heat  the  sulphur,  to  the  amount  of  from  3%  to  60%, 
is  thoroughly  mixed  with  the  crude  rubber.  As  sulphur 
fuses  at  about  113  deg.  C.,  it  is  necessary  to  subject 
the  sulphur  impregnated  rubber  to  a  heat  of  at  least  this 
temperature.  It  has  been  found  by  experiment  that  when 
such  rubber  is  subjected  to  a  temperature  of  over  150  deg. 
C.,  for  any  length  of  time,  the  mass  shows  a  tendency 
to  carbonize  and  harden.  So  for  all  practical  purposes 
the  temperatures  are  kept  between  130  deg.  and  140  deg. 
C.  relying  on  the  length  of  time  to  produce  the  de- 
sired hardness  or  density  in  the  finished  article.  In  the 
manufacture  of  hard  rubber  the  mass  is  sometimes  vul- 
canized at  a  temperature  of  160  C.  for  six  or  seven 
hours. 

In  the  manufacture  of  rubber  goods,  the  purposes  for 
which  the  article  is  intended  must  be  taken  into  con- 
sideration. Where  soft,  pure  rubber  would  work  to  ad- 
vantage in  one  place,  it  would  prove  a  failure  in  another. 
It  can  be  readily  seen  that  while  a  pure,  elastic,  rubber 


RAW    MATERIALS  55 

stock  would  act  to  advantage  in  flexible  insulating  tubes, 
the  same  stock  would  prove  a  disadvantage  in  the  mold- 
ing of  solid  insulators.  Consequently,  certain  chemicals 
and  minerals  in  addition  to  the  variable  proportions  of 
sulphur  are  incorporated  with  the  crude  rubber,  this 
admixture  depending  upon  the  purpose  for  which  it  is 
to  be  used. 

When  the  finished  article  is  intended  to  resist  heat. 
as  for  electric  insulation,  minerals  which  are  known  to 
possess  heat-resisting  qualities,  such  as  asbestos  or  other 
inorganic  fillers,  are  added  in  greater  or  lesser  quanti- 
ties. 

Hard  rubber  or  ebonite  is  prepared  in  practically  the 
same  way  as  vulcanized  rubber.  Sulphur  to  the  amount 
of  30%  and  sometimes  over  50%  is  added  to  the  crude 
rubber  and  it  is  subjected  to  a  temperature  of  over 
150  deg.  C.  for  several  hours. 

As  an  electrical  insulator,  rubber  must  be  rated 
highly.  It  has  been  found  that  rubber  in  its  unvulcanized 
state  has  a  higher  dielectric  strength  than  after  being 
vulcanized  and  that  compounding  with  chemicals  and 
minerals  decreases  this  property  in  proportion  to  the 
percentage  of  chemicals  and  minerals  used. 

Inasmuch  as  sulphur  is  also  a  good  insulator,  crude 
rubber,  mixed  with  sulphur  alone,  is  sometimes  used 
for  electrical  work,  but  on  account  of  the  cost  of  the 
rubber  compounding  to  the  extent  of  50%  to  90%  is 
often  resorted  to. 

While  many  substitutes  for  rubber  have  been  offered, 
they  lack  the  excellent  toughness  and  elasticity  which 
rubber  possesses  and  till  these  substitutes  can  be  pro- 
duced possessing  these  qualities  and  at  a  lower  cost 
than  rubber,  the  latter  will  continue  to  hold  its  own. 

Vast   amounts   of  money   and   effort  have  been    ex- 


56  MOLDED    INSULATION 

pended  throughout  the  civilized  world  in  attempts  to 
produce  rubber  by  artificial  means  and  it  seems  as  if 
at  last  success  was  in  sight. 

These  efforts  have  for  some  time  past  centered  on 
the  cheap  production  of  isoprene,  the  essential  constituent 
of  India  rubber. 

The  new  process  from  which  so  much  is  expected,  is 
based  on  using  starch  as  an  initial  raw  material,  pro- 
ducing therefrom  amylalcohol  by  a  process  of  fermenta- 
tion and  converting  the  amylalcohol  by  certain  chemical 
manipulations  into  the  unsaturated  hydrocarbon  isoprene. 

Isoprene  had  previously  been  produced  from  various 
s'ubstances,  such  as  from  turpentine,  acetylene,  and 
ethylene,  but  due  to  the  high  and  fluctuating  cost  of 
these  materials,  the  production  of  synthetic  rubber  had 
not  made  any  remarkable  progress  until  the  discovery 
of  a  method  of  deriving  isoprene  from  so  simple,  cheap, 
and  readily  obtainable  a  material  as  starch. 

Isoprene  when  properly  treated  will  polymerize  into 
rubber.  . 

The  process  here  referred  to  is  comparatively  new 
and  it  is  too  soon  to  make  positive  predictions  as  to  the 
success  of  this  very  interesting  development  in  this  im- 
portant art,  but  the  future  of  a  process  depending  on 
so  cheap  and  simple  a  raw  material  is  full  of  promise 
and  it  looks  as  if  the  goal  for  which  so  many  investiga- 
tors have  so  tirelessly  striven  is  at  last  almost  attained. 


FORMALDEHYDE 

Formaldehyde  (Methylaldehyde,  or  Methanal)  H.COH 
is  the  oxydation  product  of  Methylalcohol  CH3OH  and 
the  Aldehvde  of  Formic-acid  HCOOH  It  is  the 


RAW   MATERIALS  57 

simplest  type  of  all  Aldehydes,  the  latter  being  the  oxyda- 
tion  products  of  the  primary  alcohols.  This  may  be  shown 
in  the  following  schemes : 

/H2  7H 

R,C<  R.C/ 
XOH  X0 

Prim.  Alcohol  Aldehyde 

/H,  /O 

H.0<  H.C< 

x  OH  XH 

Methylalcohol  Formaldehyde 

"R"  Indicating  any  organic  radical  or  element  what- 
ever. Though  Formaldehyde  was  discovered  as  early 
as  1867,  and  although  its  important  functions  in  the 
process  of  assimilation  in  plant  life  has  been  recognized 
by  prominent  chemists  for  many  years,  its  technical  use 
and  manufacture  on  a  large  scale  dates  back  only  to 
about  1886. 

Formaldehyde  at  ordinary  temperatures  is  a  gas  of 
pungent  smell,  which  at  — 21-deg.  C.  condenses  to  a  color- 
less liquid.  In  commerce,  it  usually  occurs  in  a  watery 
solution  of  about  35%  to  40%,  which  is  known  under  the 
technical  term  of  " FORMALIN,"  or  in  its  polymerized 
and  solid  forms  as  the  so-called  "PARAFORM"  (HCHO)2 
or  as  "TRIOXYMETLIYLENE  (HCHO)3. 

Formalin,  however,  is  the  usual  commercial  form 
of  Formaldehyde. 

By  the  incomplete  oxydation  of  methylalcohol,  the 
latter  being  mixed  with  air,  in  the  presence  of  any  contact 
substance  (catalyser)  usually  granulated  copper,  Form- 
aldehyde is  produced  as  an  intermediate  product  between 
methylalcohol  on  the  one  hand  and  formic  acid  on  the 
other  hand.  This  process  formulated  in  the  equation: 
CHa  OH+O=HCOH+H20 


58  MOLDED   INSULATION 

is  at  the  present  time  the  usual  way  of  manufacturing- 
Formalin. 

On  further  oxydation  Formaldehyde  yields  formic- 
acid  and  finally  carbonic-acid: 

HCOH+0=HCOOH 
HCOOH+0=CO2+H2b 

The  oxydation  with  copper  as  a  catalyser  starts  at 
a  temperature  below  300-deg.  C.  By  carefully  watching 
the  temperature  and  not  allowing  it  to  rise  too  far  above 
300-deg.  C.,  the  quantity  of  carbonic  acid  produced  will 
be  negligible.  The  methylalcohol  present  in  excess  in 
the  watery  Formaldehyde  solution  is  separated  from  the 
latter  by  fractional  distillation  in  column  dephlegmators. 

The  aqueous  formaldehyde  solution  of  commerce, 
however,  contains  about  10%  of  methylalcohol,  which 
prevents  the  polymerization  of  the  formaldehyde. 

Formalin,  like  the  gaseous  formaldehyde,  has  a  pun- 
gent odor  and  shows  frequently  a  slightly  acid  reaction 
due  to  the  formation  of  traces  of  HCOOH.  The  specific 
gravity  of  formalin  of  the  usual  commercial  strength 
of  35-^0%,  is  1.081  to  1.097. 

A.  few  other  processes  of  more  scientific  interest 
may  be  briefly  mentioned  here. 

If  a  mixture  of  methan  CH4  with  a  quantity  of 
air  insufficient  for  a  complete  oxydation,  is  passed  over 
glowing  copper  or  asbestos,  formaldehyde  is  produced. 

Formic  acid  is  transformed  into  formaldehyde  by 
mixing  the  acid  vapors  with  hydrogen  and  passing  this 
mixture  over  iron,  nickel,  zinc  or  other  metals,  at  high 
temperatures. 

By  evaporating  an  aqueous  solution  of  formaldehyde, 
paraformaldehyde  (HCOH)2  is  produced  as  a  white  am- 
orphous mass,  which  on  drying  passes  into  the  other  modi- 


RAW    MATERIALS  59 

fication,  trioxymethylene  (HCOH)3.  This  body  is  volatile 
at  180 — 200-deg.  C.  turning  into  formaldehyde  again. 

Formaldehyde,  as  the  first  and  lowest  type  of  the 
aldehydes  possesses  an  enormous  capability  to  undergo 
reactions  with  other  compounds,  even  with  such  compara- 
tively indifferent  bodies  as  kerosene  oil  or  benzol. 

Formaldehyde  precipitates  mercury  and  bismuth  in 
alkaline  solution.  It  reduces  silver  even  in  its  insoluble 
chloride,  and  silver  mirrors  are  made  by  the  action  of 
gaseous  ammonia  upon  a  paste  of  silversalt — formalin. 

With  ammonia  and  formaldehyde  hexamethylene- 
tetra-amine  C0H12N4  is  formed.  When  boiled  with  lime- 
water  it  yields  formic-acid  and  an  amorphous  saccharine 
substance — methyl  enitan. 

Its  condensing  reactions  are  very  numerous,  and 
it  is  chiefly  due  to  this  circumstance  that  its  technical 
application  has  increased  so  enormously  within  the  last 
twenty  years. 

Formaldehyde  condenses  with  dimethylamin  into 
tetramethyl-diamidodiphenylmethan,  the  raw  material  of 
the  leuko-base  of  Krystallviolet.  Also  other  dyestuffs 
like  parafuchsin,  rieufuchsin,  etc.,  are  made  by  means  of 
formaldehyde. 

Besides  its  use  as  a  disinfecting  material  instead  of 
phenol  and  mercury  bichloride,  it  finds  a  large  applica- 
tion as  a  preservative  for  crude,  raw  products,  in  tan- 
neries, soap  works,  etc.  It  is  often  added  to  glues,  gums, 
or  starch  solutions  for  a  similar  purpose. 

Its  applications  in  many  industries,  such  as  in  photog- 
raphy, leather  making,  and  in  the  manufacture  of  india 
rubber  goods,  etc.,  are  very  great.  It  condenses  with 
phenols  producing  resin-like  bodies,  which,  besides  being 
the  raw  materials  of  many  substitutes  for  amber,  hard 
rubber,  bone,  etc.,  have  proved  to  be  substances  of  high 


60  MOLDED    INSULATION 

insulating  power,  wherefore,  this  condensation  reaction 
of  formaldehyde  with  phenols  will  be  treated  in  this  book 
in  a  special  chapter  under  "CLASS  'G.'  " 


PHENOL 

Phenol  is  the  type  of  a  series  of  organic  compounds 
which  form  a  class  by  themselves  as  derivatives  of  the 
so-called  aromatic  compounds,  the  latter  having  as  their 
representatives  benzene  or  benzol. 

As  the  chemical  structure  of  both  bodies  readily 
shows,  phenol  results  theoretically  from  the  substitu- 
tion of  one  H-atom  in  the  benzol  nucleus  through  the 
hydroxyl — or  OH  group — this  radical  being  the  typical 
chemical  characteristic  of  all  phenols. 

"Whereas  phenol  itself,  as  the  first  representative  of 
the  phenol  group,  contains  only  one  OH  radical,  it  is 
possible  to  substitute  gradually  all  6  H-atoms  in  the 
benzol  nucleus,  thus  arriving  at  higher  phenols. 

Since  the  H-atom  of  the  phenol — OH  group,  is  of  a 
more  electro-negative  character  than  the  hydrogene  of 
the  alcohol-OH  group,  we. may  consider  the  phenols  as 
a  group,  standing  between,  the  alcohols  and  the  acids. 
This  explains  the  term  carbolic  acid  used  sometimes  in- 
stead of  the  more  scientific  name  "PHENOL." 

Phenol,  discovered  in  1834  by  Runge,  occurs  very 
widely  in  the  animal,  as  well  as  vegetable  kingdom.  As 
a  product  of  the  change  of  matter  in  the  human  and 
animal  body  it  occurs  in  the  urine.  Furthermore,  phenol 
or  its  homologues,  is  formed  by  the  decay  of  albumin, 
ty rosin  and  the  like,  and  especially  by  the  destructive 
distillation  of  organic  compounds,  as,  for  instance,  wood 
and  bones,  also  by  the  dry  distillation  of  bituminous  and 


RAW    MATERIALS  61 

anthracite  coal.  It  occurs  in  the  needles  and  sap  of -pine 
wood,  in  mineral  oils,  and  is  technically  one  of  the  most 
important  constituents  of  coal  tar,  the  latter  being  the 
main  source  of  its  manufacture.  Although  synthetic 
methods  of  manufacturing  phenol  are  well  known,  its 
production  from  coal  tar  is  still  the  most  usual  and 
economical  way. 

As  the  phenol  is  soluble  in  caustic  alkali,  it  can  easily 
be  isolated  from  coal  tar  by  agitating  the  latter  in  the 
solutions  of  the  former.  Acids  will  then  separate  the  free 
phenol  from  the  solution,.  The  phenol  itself  is  then  puri- 
fied by  fractional  distillation. 

The  chemical  part  of  this  comparatively  simple  pro- 
cess is  shown  by  the  equations : 

C0H5OII+NaOH:=C6H5ONa+H20 
2C0H5ONa-fH2S04=2C0H5OH+Na2S04 

Phenol  is  also  soluble  in  concentrated  sulphuric  acid, 
thus  forming  sulphonic  acid. 

Due  to  this  reaction,  practical  manufacturing  pro- 
cesses have  been  introduced  to  separate  phenol  from  the 
tar  oils ;  although  their  yield  is  not  quite  as  satisfactory 
as  that  produced  by  the  alkali  method. 

Of  the  synthetic  processes  of  producing  phenol,  two 
may  be  mentioned  on  account  of  their  greater  importance 
in  the  art. 

They  are  the  methods  of  Griess,  and  Kekule,  Wurtz 
and  Dusart. 

Griess  produced  phenol  on  a  large  scale  by  boiling 
the  diazocompound  of  aniline  diluted  acids. 

Kekule,  Wurtz,  and  Dusart  have  found  independently 
of  each  other,  that  benzolsulphonic  acid  is  turned  into 
phenol  and  potassium-bisulphite  by  fusing  it  with 


62  MOLDED    INSULATION 

potassium  hydroxyd,  the  chemical  reaction  being  as  fol 
lows: 

C0H5SOsNa+NaOH=CeH5pNa4-NaHS03 

This  synthesis  especially  was  successfully  applied  for 
some  time  when  the  market  price  of  phenol  was  high 
enough  to  permit  it.  The  resulting  phenol  showed  a 
remarkable  purity  and  a  somewhat  weaker  and  more 
pleasant  odor.  But  as  the  same  result  is  now  obtained  in 
a  cheaper  way  by  the  production  of  phenol  from  coal  tar, 
as  mentioned  above,  the  synthetic  methods  are  nowadays 
almost  entirely  abandoned. 

In  a  pure  state,  phenol  crystallizes  in  long  white 
needles,  which  melt  at  42.2-deg.  C.,  and  boil  without  be- 
ing decomposed  at  183 — 184-deg.  C.  Ordinary  phenol, 
however,  melts  somewhat  lower,  usually  at  35.5 — 40.5-deg. 
C.,  due  to  traces  of  cresol  or  water.  The  specific  gravity 
of  phenol  at  18-deg.  C.,  is  1.065. 

Owing  to  its  hygroscopic  qualities,  phenol  exposed 
to  moist  air,  takes  up  a  considerable  amount  of  water 
and  the  melting  point  is  lowered. 

Though  hygroscopic,  phenol  itself  is  not  very  readily 
soluble  in  water,  one  part  of  phenol  dissolving  in  20 
parts  of  water  at  ordinary  temperatures.  Other  solvents 
like  alcohol,  ether,  benzol,  glacial  acetic  acid  and 
glycerine,  on  the  other  hand,  dissolve  phenol  in  all  pro- 
portions. 

Phenol  can  be  extracted  from  its  watery  solution 
with  benzol,  ether,  carbon  disulphide  or  chloroform.  The 
watery  solution  does  not  redden  litmus. 

Phenol  has  a  peculiar  smokelike  smell,  it  attacks  the 
skin  very  violently  and  is  poisonous  in  its  internal  effects, 
due  to  its  property  of  coagulating  albumin. 

Of  its  many  characteristic  reactions  the  more  im- 
portant ones  may  be  mentioned. 


RAW   MATERIALS  63 

Ferichloride,  not  in  excess,  gives  a  violet  color  with 
one  part  of  phenol  solution  to  3,000  parts  of  water. 

Twenty  cc  of  a  solution  of  phenol  to  5,000  parts  of 
II2O  show  on  gradual  heating  with  ammonia  and  Eau  De 
Javelle,  a  deep  blue  color,  which  is  changed  by  the  action 
of  acid,  to  red. 

Phenol,  added  to  a  solution  of  nitrous  acid  in  sul- 
phuric acid,  gives  gradually  a  brown,  then  a  golden,  and 
finally  a  blue  color. 

Another  very  important  reaction  of  phenol  consists 
in  its  behavior  when  treated  with  bromine  water.  A 
watery  solution  of  phenol,  with  a  freshly  prepared  solu- 
tion of  bromine  water,  gives  a  bulky,  white,  precipitate, 
even  in  solutions  up  to  1  :  40000  or  50000.  Upon  this 
reaction  a  quantitative  method  of  determining  phenol  is 
based. 

The  reaction  of  phenol  with  formaldehyde  and  its 
different  modifications  are  of  very  great  interest  and  the 
resulting  products  will  be  dealt  with  in  further  articles 
under  "Condensation"  and  "Synthetic  Resinous  Pro- 
ducts" (Class  G). 


CONDENSATION 

Condensation  is  a  special  form  of  the  many  synthet- 
ical reactions  applied  in  organic  chemistry. 

The  simplest  form  of  a  condensation  takes  place 
when  two  molecules  of  the  same  or  different  organic 
compounds  unite  under  proper  conditions  by  means  of 
carbon  linkings,  whereby  one  or  more  molecules  of  water 
are  eliminated,  and  a  more  complicated  compound  of  a 
higher  carbon  content  is  formed.  This  newly  formed 
body  is  termed  a  condensation  product,  and  it  is  usually 


64  MOLDED    INSULATION 

impossible  to  decompose  it  into  its  original  components. 
Generally  some  condensing  agents,  as  for  instance  H2SO4, 
ZnCl2,  anhydrides,  caustic  alkalies,  ammonia  and  its  de- 
rivatives, which  are  capable  of  splitting  off  H20,  are  ap- 
plied, thus  causing  the  condensation  reaction  whereby 
one  of  the  substances  loses  oxygen,  whereas  the  other  one 
splits  off  hydrogen  as  shown  in  the  equation. 

CH3CHO+CH3CHO=CH3CH  :CH.CHO-f  H20 

Acetaldehyde  Acetaldehyde  Crotonaldehyde  Water 

Sometimes,  however,  morfi  than  two  molecules  of 
the  same  or  different  substances  may  combine,  with 
separation  of  H2O. 

C6PT5CHO-f2C6H5NH2=  C6H5CH  (C6H4NH2)2+H20 

Benzaldeliyde  Aniline  Diamidotriphenylmethan  Water 

In  other  condensations,  elimination  of  HC1;  NH3  or 
even  C(X  may  take  place.  To  the  latter  reaction  belongs 
the  well-known  process  of  producing  Ketones  by  heating 
calcium  salts  of  organic  acids. 

(CH3  COO)2  Ca=CH3  COCH3+CaCo3 

Calcium  Acetate  Acetone  Calcium  Carbonate 

Also  by  means  of  an  oxydation  a  condensation  re- 
action may  be  produced. 

Phenols  containing  one  OH  group,  for  instance,  when 
treated  with  ferric  chloride,  lose  one  atom  of  hydrogen 
and  turn  into  higher  phenols  containing  two  OH  groups 
and  the  double  amount  of  carbon  atoms: 

2C10H7OH+2FeCl3=C20H12  (OH)2+2HCl+2FeCl2 

Naphthol  Dinaphthol 

Aldehydes  and  especially  ketones  are  very  liable  to 
condensation  reactions,  whereby  complicated  compounds 
of  very  high  molecular  weights  are  frequently  produced. 

The  same  process  we  probably  encounter,  according 
to  more  recent  discoveries,  in  the  formation  of  resins  in 


RAW   MATERIALS  65 

plant  life,  the  latter  being  very  likely  condensation  pro- 
ducts of  formaldehyde  with  phenol. 


66  MOLDED    INSULATION 


THE  HOT  MOLDED  ORGANIC  MATERIALS 
(Class  "A") 


The  ingredients  of  sealing  wax  and  of  this  class  of 
molded  insulation  have  not  varied  from  their  earliest 
history. 

The  binders  play  the  important  part  in  this  class  of 
materials,  the  principal  ingredient  of  which  once  was, 
and  still  ought  to  be,  shellac. 

Owing,  however,  to  the  steady  increase  in  the  price 
of  shellac,  it  has  been  replaced  almost  entirely  by  cheaper 
materials,  such  as  damar  gum,  rosin,  asphalts,  pitches 
and  cheap  resins. 

Two  methods  are  employed  to  combine  these  binders 
with  such  fillers  as  wood  pulp,  magnesia,  lime,  sand  and 
asbestos,  and  such  coloring  matters  as  lamp  black,  various 
metallic  or  earth  pigments,  and  organic  dye  stuffs. 

First :  The  organic  binders  are  placed  in  a  heated 
mixing  machine  in  which  they  are  melted,  and  when 
in  a  molten  condition,  the  binders  are  gradually  added 
and  mixed.  The  mixture  is  then  removed  in  a  hot  plastic 
condition  and  rolled  into  sheets.  These  sheets  are  broken 
into  convenient  sizes,  softened  on  steam  tables  and  then 
placed  in  heated  dies,  pressed,  cooled  therein,  and  re- 
moved in  a  finished  condition.  The  dies  in  this  method 
are  the  open  dies,  described  more  fully  under  the  chapter 
11  Moulds  and  Dies." 

In  the  second  method  employed  in  molding  this 
class  of  products  the  organic  binding  materials  are  dis- 


HOT  MOLDED  ORGANIC  MATERIALS        67 

solved  in  proper  solvents  and  the  mass  mixed  with  the 
filler  in  about  the  same  kind  of  mixing  machines  as  in 
the  first  method,  except  that  no  heat  is  employed.  The 
material  is  removed  from  the  mixing  machine  and  on 
exposure  to  the  air  the  solvents  evaporate,  leaving  an 
intimate,  uniform,  mixture.  This  mass  having  become 
hard  is  ground  to  powder.  The  powder  is  then  placed 
in  heated  dies  in  which  it  remains  under  pressure  until 
it  is  melted,  it  is  then  cooled  and  removed  from  the  die 
in  a  finished  condition. 

The  dies  used  in  this  method  are  called  "closed 
dies."  This  type  of  die  is  explained  under  the  chapter 
"Molds  and  Dies." 

Manufacturers  of  products  of  this  class  vary  the 
minor  details  of  the  processes  of  manufacture,  but  all 
follow  one  of  the  two  above  mentioned  fundamental 
methods. 

Materials  produced  by  either  of  these  two  methods 
differ  but  little  in  their  properties.  The  second  method, 
however,  allows  the  incorporation  of  more  filling  ma- 
terial. 

In  the  first  method,  the  amount  of  filler  which  can 
be  added  is  restricted,  for  if  too  much  is  used,  the  plastic 
nature  of  the  mix  is  diminished  and  the  material  will  not 
flow  properly  in  the  die. 

The  second  method  is  free  from  this  difficulty,  for  the 
material,  being  in  a  powdered  form,  can  be  readily  in- 
troduced into  the  dies,  which  are  of  such  design  that  the 
material  cannot  ^escape,  but  is  forced  to  all  parts  of  the 
die,  and  intimately  welded  together  by  the  pressure. 

The  higher  the  proportion  of  binding  material,  and 
the  more  finely  reduced  the  filler,  the  more  plastic  the 
mix  will  be,  and  the  cleaner  the  .appearance  of  the  finished 
piece. 


68  MOLDED   INSULATION 

On  the  other  hand,  the  higher  the  percentage  of 
filler,  especially  when  the  filler  is  inorganic,  the  less 
plastic  the  mix  will  be  and  the  poorer  the  appearance 
of  the  finished  piece,  but  it  will  be  less  subject  to  the 
softening  influence  of  heat,  which  constitutes  a  serious 
defect  in  materials  of  this  class. 

The  composition  of  material  of  this  class  varies  over 
a  wide  range,  and  the  characteristics  differ  accordingly. 

If  the  binder  is  entirely  free  from  rosin  or  cheap 
gums,  these  products  are  very  stable  and  their  life  is  long. 
Unfortunately,  however,  the  general  trend  for  the  past 
ten  years  has  been  to  substitute  rosin  and  dammar  gum 
for  shellac,  which,  especially  in  case  of  rosin,  due  to  its 
well-known  unstable  qualities,  will  cause  the  compound 
to  deteriorate  rapidly  under  climatic  exposure. 

However,  rosin  is  extensively  used  because  of  its 
low  price,  and  the  advantage  it  possesses  of  being  rapidly 
melted  and  molded  at  comparatively  low  temperatures. 
in  which  respect  it  is  the  best  substitute  for  shellac. 
All  other  substitutes  have  the  objection  of  requiring 
higher  temperature  to  melt,  and  not  being  so  readily 
molded  in  dies. 

It  should  be  stated  here  that  a  certain  variety  of 
bitumens  or  asphalts  melt  very  easily,  but  pieces  made 
with  such  binders  do  not  withstand  any  great  tempera- 
ture. In  some  cases,  these  products  have  been  known 
to  soften  under  the  rays  of  the  sun. 

Materials  of  this  class,  when  proper  ingredients  are 
employed,  are  practically  non-hygroscopic,  and  moisture 
has  no  detrimental  effect  on  their  physical  or  chemical 
properties.  It  might  be  mentioned  that  products  of 
this  class,  containing  a  great  excess  of  fillers,  for  in- 
stance, asbestos  fibre,  will  absorb  more  or  less  water, 
but  these  products,  if  properly  made,  even  though  they 


HOT  MOLDED  ORGANIC  MATERIALS        69 

absorb  moisture  to  a  certain  extent,  are  sufficiently  im- 
pervious under  ordinary  weather  conditions  for  use  for 
ordinary  voltages,  if  they  contain  no  rosin. 

As  none  of  the  ingredients  undergo  any  chemical 
change  in  the  processes  employed  in  the  manufacture  of 
these  products,  it  is  perfectly  obvious  that  they  will 
always  soften  at  the  temperature  to  which  they  are 
subjected  in  their  mixing  or  molding  processes.  For 
instance,  articles  made  with  shellac,  which  softens  at  80° 
C.,  will  not  withstand  temperatures  above  this  point. 
Kosins,  which  stand  less,  and  materials  made  with  soft 
bitumens,  will  soften  in  the  sun's  rays  in  hot  weather. 
This  is  particularly  true  if  the  binders  are  in  great 
excess  in  the  mixture. 

Such  materials  can  be  made  so  that  they  will  with- 
stand a  momentary  flame,  and  if  not  subjected  to  heat 
for  too  long  a  time,  they  will  not  readily  soften,  but 
they  will  invariably  fail  as  soon  as  a  continuously  ap- 
plied temperature  reaches  the  melting  point  of  the  bind- 
ing medium. 

The  insulating  properties  of  this  class  of  materials 
vary  very  materially.  For  instance,  one  specimen 
.001  inch  thick  may  be  punctured  by  500  volts, 
while  another  specimen  of  the  same  thickness  will  be 
punctured  by  50  volts. 

The  reason  for  this  great  difference  lies  in  the  wide 
variation  in  the  composition  of  materials  of  similar  ap- 
pearance. The  higher  the  percentage  of  organic  binder, 
the  better  the  insulating  properties;  the  lower  the 
percentage  of  binder,  and  the  higher  the  percentage  of 
filler,  the  poorer  the  insulating  qualities  will  be.  The 
more  intimate  the  mixture  between  the  filler  and  binder 
and  the  higher  the  pressure  under  which  it  is  molded  in 
the  proper  plastic  condition,  the  less  porous  the  product 


70  MOLDED   INSULATION 

will  be,  and  consequently  the  higher  its  resistance  to 
puncture. 

The  use  of  such  materials  for  electrical  insulation 
has  somewhat  diminished  because  these  products  do  not 
withstand  heat.  They  are  liable  to  become  inflamed  by  the 
short  circuiting  of  wires  carrying  low  voltages,  and  the 
Underwriters  are  steadily  becoming  more  and  more  strict 
and  are  specifying  materials  of  greater  heat-resisting 
qualities. 

The  field,  however,  for  this  class  of  materials  is 
still  very  large,  and  from  the  following  illustrations, 
it  will  be  seen  to  what  a  wide  range  of  uses  in  the  elec- 
trical art,  these  materials  are  still  adapted. 

Several  concerns,  both  here  and  abroad,  have,  after 
long  study  and  experiments,  been  able  to  produce  pieces 
suitable  for  high  tension  insulation,  and  they  claim 
considerable  advantages  for  these  substances  over  por- 
celain for  high  tension  work.  The  discussion  of  insulation 
for  high  tension  work  is  not  within  the  province 
of  this  work,  and  therefore  these  special  shellac  com- 
pounds will  not  be  treated  here  in  detail.  It  may  be  said 
in  passing,  however,  that  this  material  has  been  com- 
mercially produced  for  this  purpose,  although  the  bulk 
of  insulation  of  this  kind  is  still  made  in  porcelain. 


COLD  MOLDED  ORGANIC  MATERIALS  3    71 


COLD  MOLDED  ORGANIC  MATERIALS 
(Class  "B") 


Molded  insulating  products  of  this  class  are  similar 
in  appearance  to  those  of  Class  "A,"  and  chemical 
analysis  would  show  that  they  are  composed  of  an  organic 
binder  and  an  inorganic  filler,  as  are  most  of  the 
materials  of  that  class.  The  usual  binders  employed  in 
the  manufacture  of  these  products  are  the  asphalts,  and 
the  fillers  are  such  inorganic  substances  as  asbestos,  silica, 
and  magnesia,  organic  fillers  being  but  rarely  employed. 
In  color  they  are  universally  black,  due  to  the  asphalts 
used  in  their  composition. 

A  fundamental  and  very  important  difference  be- 
tween materials  of  this  class  and  those  of  Class  "A"  is 
that  the  incorporation  of  the  filler  with  the  binder  and 
the  subsequent  molding  is  not  done  under  heat,  but  the 
binding  medium  is  brought  into  solution  by  suitable 
solvents,  and  the  filler  thoroughly  mixed  with  the  liquid 
or  semi-liquid  binders  in  a  cold  condition.  This  semi- 
plastic  mixture  is  then  molded  in  cold  dies,  care  being 
required  to  have  the  material  sufficiently  soft  to  mold 
properly.  The  pressed  pieces  are  then  subjected  to  a 
drying  process,  during  which  the  solvents  are  drawn 
off  or  enter  into  composition  with  the  other  constituents, 
whereby  a  hard,  solid  and  durable  substance  is  obtained. 

The  making  of  materials  by  this  process  presents 
some  manufacturing  disadvantages,  for  instance,  during 
the  drying  process,  they  are  subject  to  a  slight  shrink- 


72  MOLDED   INSULATION 


age,  unlike  articles  molded  of  the  materials  of  Classes 
"A"  and  "G,"  which  come  from  the  dies  in  a  finished 
condition.  For  this  reason  a  slight  variation  of  the 
finished  pieces,  from  exact  dimensions,  should  always  be 
allowed  as  is  customary  with  users  of  porcelain.  How- 
ever, as  the  shrinkage  incident  to  the  drying  of  these 
materials  is  only  one-eighth  that  which  takes  place  in  the 
firing  of  the  ceramic  products  (porcelain)  they  can  be 
depended  upon  for  greater  degree  of  accuracy  than  those 
of  Class  "D." 

In  fact,  the  art  of  manufacturing  these  cold  molded 
inorganic  materials  has  undergone  such  development  dur- 
ing the  last  ten  years  as  to  make  it  entirely  practicable 
to  mold  such  materials  with  sufficient  accuracy  to  fully 
meet  the  demands  of  commercial  conditions. 

The  products  of  this  class  are  not  manufactured  in 
such  a  great  variety  of  grades  as  those  of  Class  "A"  and 
while  the  insulating  properties  of  different  materials 
of  this  class  vary,  their  use  is,  as  yet,  restricted  to  the 
manufacture  of  parts  for  low  tension  insulation. 

One  of  the  chief  advantages  of  these  products  and 
one  to  which  is  due  their  wide  favor  among  electrical 
engineers  is  that  they  are  exceedingly  stable,  and  once 
manufactured  will  not  soften  under  heat,  and  moisture 
has  little  effect  upon  their  physical  or  electrical  properties. 

In  Class  "A"  it  is  the  binder  which  is  always  the  im- 
portant part,  whereas  in  materials  of  Class  "B"  it  is 
the  filler — the  asbestos  fibre  which  imparts  to  the  pro- 
duct its  main  advantages,  the  binder  performing  the 
functions  of  cementing  and  waterproofing  media. 


COLD  MOLDED  INORGANIC  MATERIALS     73 


THE   COLD   MOLDED   INORGANIC   MATERIALS 
(Class  "-C") 


Materials  of  this  class  differ  from  those  of  Class 
"A"  and  "B"  in  the  characteristic  principle  of  the  use 
of  an  inorganic  binder,  while  in  Classes  "A"  and  "B" 
an  organic  binding  media  is  used. 

The  binders  of  this  class  are  compounds  of  silica, 
alumina,  lime  and  magnesia,  or  usually  Portland  Cement, 
while  the  filler  is  usually  asbestos  fibre. 

The  use  of  hydraulic  cements  for  such  purposes  was 
retarded  for  years,  due  to  its  poor  plasticity,  but  during 
the  last  ten  years  great  progress  has  been  made  in  this 
direction,  and  today  they  are  extensively  used  as  binders 
for  materials  of  this  class. 

Its  use  as  a  binder  is,  however,  a  critical  one,  and 
not  only  must  the  cement  be  selected  with  great  care 
to  assure  its  fitness,  but  in  the  manufacturing  operation 
several  well  defined  steps  are  necessary  in  order  to  obtain 
a  properly  plastic  material. 

The  main  difficulties  consist  in  the  proper  incorpora- 
tion of  reagents  to  develop  the  plasticity  of  the  mixture 
without  injury  to  same.  Their  action  is  yet  not  thorough- 
ly understood,  but  possibly  it  is  of  a  catalytic  nature. 

Broadly  speaking,  the  binder  is  incorporated  with 
the  filler  in  the  presence  of  water,  and  the  moist  mixture 
is  pressed  in  a  cold  state  in  dies  under  heavy  pressure, 
whereby  the  excess  of  water  is  eliminated  and  the  molded 
pieces  are  given  a  consistency  which  permits  them  to 


74  MOLDED    INSULATION 

be  removed  from  the  dies.  The  hardening  of  the  mold- 
ings afterwards  is  effected  by  the  action  of  the  hydraulic 
binders  in  a  similar  way  to  the  hardening  of  Portland 
Cement. 

Such  insulating  products,  owing  to  the  inorganic 
nature  of  both  binder  and  fillers,  are  unaffected  by  heat 
and  the  electric  arc,  and  by  various  treatments  they  are 
rendered  non-absorbent  to  moisture. 

The  appearance  of  materials  of  this  class  is  not  as 
attractive  as  that  of  materials  of  Classes  "A,"  "B,"  "G" 
and  "E,"  but  their  physical  properties,  owing  to  the 
nature  of  the  inorganic  binder,  possess  the  peculiar  ad- 
vantages of  rather  improving  in  quality  with  age,  as 
do  all  materials  of  concrete  nature  containing  hydraulic 
binding  media. 

Both  binders  and  fillers  play  an  equally  important 
part  in  the  compounding,  and  the  mechanical  properties 
of  the  finished  articles  depend  to  a  considerable  degree 
on  the  structure  of1  the  asbestos  fibre  used  as  a  filler. 


CERAMICS  75 


CERAMICS 
(Class  "D") 

This  class  is  usually  known  under  the  broad  term 
of  "CERAMICS,"  the  most  familiar  representative  being 
porcelain.  Other  materials  of  this  class  are  glass,  fused 
silica,  fused  clay  and  roasted  soapstone  (Lavite). 


PORCELAIN 

The  so-called  hard  porcelain  is  of  the  most  impor- 
tance for  electrical  uses.  Hard  porcelain  comprises  a 
large  percentage  of  China  Clay,  to  which  is  added 
quartz  and  feldspar  or  other  flux,  and  sometimes  small 
percentages  of  gypsum,  chalk,  etc.  The  quality  of  the 
China  Clay  used,  is  of  first  importance,  for  on  this  is 
dependent  the  plasticity  of  the  mixture,  which  enables 
it  to  be  molded  in  the  desired  forms,  and  also,  to  a 
large  extent,  the  final  hardness,  strength  and  heat-resist- 
ing qualities  of  the  product.  The  proportions  in  which 
these  ingredients  are  used  vary  with  different  manufac- 
turers, each  of  whom  has  developed  a  formula  by  which 
proper  results  can  be.  obtained.  Great  care  is  necessary  in 
each  step  of  the  manufacturing  process,  from  the  mixing 
of  the  ingredients  to  the  annealing  of  the  products  as  they 
come  from  the  kiln.  A  slight  relaxation  of  care  at  any 
one  stage  is  more  likely  to  endanger  the  quality  of  por- 
celain than  of  other  molded  insulating  products. 

In   the   manufacture    of  porcelain   the   various   raw 


76  MOLDED    INSULATION 

materials  in  proper  proportion  are  mixed  in  rotating 
drums  in  the  form  of  a  slurry,  it  being,  of  course,  essential 
that  the  ingredients  be  in  a  finely  divided  form,  and 
in  the  case  of  the  China  Clay,  free  from  impurities.  The 
excess  water  is  removed  by  various  means,  and  the  wet 
mass  is  stored  for  some  time,  during  which  the  homo- 
geneity and  plasticity  are  improved.  In  some  plants  this 
plastic  cake  is  directly  molded  in  dies,  while  in  others  it 
is  dried,  re-ground,  mixed  with  water  and  molded.  In 
pressing  porcelain  pieces,  more  especially  when  the  walls 
are  thin,  great  care  is  necessary.  The  articles,  after 
drying,  are  burned  in  kilns  at  various  temperatures  up 
to  2,000-deg.  C.  The  temperatures  and  methods  of  firing 
vary  with  different  manufacturers,  and  great  skill  has 
been  developed  at  this  stage. 

Owing  to  the  considerable  shrinkage  of  porcelain 
in  the  firing  process,  it  is  evident  that  wide  practical 
knowledge  of  the  behavior  of  various  shapes  in  the 
kiln  is  essential  in  order  that  the  final  product  shall 
be  of  the  form  and  dimensions  originally  designed,  and 
it  is  worthy  of  remark  that  this  art  has  undergone  such 
development  as  to  enable  the  production  of  parts  of  very 
complicated  design. 


LAVA  COMPOSITION 

In  making  articles  of  this  substance,  the  waste  from 
the  cutting  up  of  slate  is  used.  The  powdered  material 
is  mixed  with  solutions  of  sodium  silicate.  The  mass 
is  dried,  powdered,  and  molded  in  dies  under  pressure 
after  the  addition  of  sufficient  water.  The  molded  articles 
are  then  fired  at  high  temperatures,  and  after  cooling 
are  again  treated  with  the  alkaline  silicate  solution  and 


CERAMICS  77 

fired  again.  This  operation  is  repeated  until  absorption 
of  the  alkaline  silicate  ceases. 

The  finished  products  are  very  hard  and  tough  and 
are  somewhat  similar  to  porcelain.  They  resist  sudden 
changes  in  heat  better  than  porcelain  and  for  certain 
insulating  purposes  are,  therefore,  more  desirable.  Their 
great  shrinkage  during  firing  and  the  consequent  diffi- 
culty in  obtaining  accuracy  in  the  finished  molded  form. 
is  their  principal  draw-back. 

Special  grades  of  lava  compositions  are  made  for 
resistance  insulators  and  for  this  purpose  have  no  superior. 


78  MOLDED    INSULATION 


RUBBER  COMPOUNDS 
(Class  "E") 


Among  the  various  materials  employed  in  the  manu- 
facture of  Molded  Insulation,  rubber  is  the  only  product 
which  in  itself,  without  the  admixture  of  a  filling  or 
strengthening  medium,  presents  all  the  desirable  quali- 
ties of  an  insulator,  combined  with  the  necessary 
mechanical  strength  and  other  requisite  physical  prop- 
erties. Its  toughness,  elasticity  and  flexibility  are  not  even 
nearly  approached  by  any  other  insulating  substance 
knowTn  today.  Therefore,  its  qualifications  as  a  binder 
for  organic  or  inorganic  fillers  are  also  unsurpassed. 
The  only  reason  why  this  excellent  insulation  as  well 
as  binder  has  been  gradually  replaced  is  its  high  price 
and  inability  to  stand  continuous  temperatures  of  100-deg. 
C.,  or  over,  even  when  properly  compounded  with  such 
heat-resisting  fillers  as  asbestos. 

In  the  chapter  on  raw  materials  will  be  found  a 
full  description  of  the  preparation  of  caoutchouc,  and 
rubber  and  their  compounding. 


ORGANIC   PLASTICS  79 


ORGANIC  PLASTICS 
(Class  "F") 

CELLULOID 


While  molded  insulating  parts  are  not  made  of  this 
material  to  any  notable  extent,  it  is  nevertheless  em- 
ployed for  this  purpose,  especially  where  ornamental  ap- 
pearance is  a  considerable  factor.  It  is  a  good  insulator 
and  can  be  molded  with  greater  facility  than  perhaps 
any  other  material,  and  were  it  not  for  its  poor  heat- 
resisting  qualities,  it  would  be  extensively  employed  for 
electrical  insulating  purposes. 

Celluloid  is  a  solid  solution  of  more  or  less  nitrated 
pure  cellulose  in  camphor,  and  is  pressed,  after  evaporat- 
ing the  various  solvents  in  the  form  of  sheets,  plates, 
blocks  or  rods.  In  this  stage  it  is  a  transparent,  elastic, 
flexible  mass  which  can  be  given  any  desired  color  by 
the  introduction  of  dye  stuffs  or  pigments. 

Before  going  into  the  details  of  the  manufacture  of 
celluloid,  the  manner  of  making  nitro-cellulose  and  the 
general  method  of  making  celluloid  will  be  briefly 
outlined. 

Nitrocelluloses  are  celluloses  which  contain  the  nitro 
group  N02,  and  are  known  as  Di,  Tri,  etc.,  up  to 
hexamitrocellulose  or  even  higher  ones,  according  to 
their  content  of  the  nitro  groups.  In  celluloid  manufac- 
ture, as  a  rule,  the  higher  nitrated  celluloses  are  used, 
commonly  known  as  "gun  cotton"  which  contain  about 
9%  to  12%  nitrogen. 


80  .MOLDED    INSULATION 

They  are  obtained  by  treating  very  pure  cellulose, 
like  tissue  paper,  purified  cotton,  flax  or  hemp  fibres, 
with  a  mixture  of  concentrated  nitric  acid  and  more  or 
less  concentrated  sulphuric  acid. 

The  proportions  of  the  two  acids  may  be  varied 
considerably.  For  instance,  three  volumes  of  nitric  acid 
Spec.  Grav.  1.517,  to  one  of  sulf.  acid  Spec.  Grav.  1.84, 
or  three  volumes  of  sulf.  acid  Spec.  Grav.  1.845,  to  one 
of  nitric  acid  1.5,  are  used. 

The  proportions  of  the  paper  and  of  the  acid  mixtures 
vary  considerably.  Furthermore,  a  different  time  of  re- 
action has  to  be  allowed  according  to  different  con- 
ditions. The  space  in  this  book  is  too  limited  to  go 
into  these  complicated  details. 

The  nitrocellulose,  purified  by  washing  with  cold 
water  until  perfectly  free  of  acid,  is  then  treated  with 
a  weak  sodium  carbonate  solution  at  ordinary  tempera- 
ture, and  the  latter  again  removed  by  washing  with  cold 
water.  The  pure  material  is  ground  to  pulp,  the  water 
extracted  in  centrifuges,  and  after  having  been  dried  at 
about  40-deg.  C.  it  is  mixed  with  a  solution  of  camphor 
in  alcohol. 

The  proportion  of  camphor  and  nitro-cellulose  varies 
from  20%  to  30%  of  camphor  and  70%  to  80%  of  nitro- 
cellulose. 

The  alcoholic  camphor  mixture  is  passed  between 
rollers  heated  to  105-deg.  C.  This  process  is  carried  on 
until  a  homogeneous  and  plastic  mass  results.  These 
rolled  celluloid  sheets  are  then  pressed  into  solid  blocks, 
free  of  air  bubbles,  under  a  pressure  of  about  3,500-lbs. 
per  square  inch. 

A  few  of  the  special  methods  employed  in  the  manu- 
facture of  celluloid  may  be  mentioned. 

1.     The  so-called  Hyatt  process  consists  in  dissolving 


ORGANIC    PLASTICS  81 

gun-cotton  in  molten  camphor.  Satin  paper  is  sprayed 
with  a  mixture  of  two  parts  nitric  acid  and  five  parts 
sulphuric  acid  as  it  is  unwound  from  a  roll,  whereby 
the  greater  part  of  the  paper  is  converted  into  nitro- 
cellulose or  pyroxylin.  The  acid  is  now  entirely  removed 
by  washing  with  water,  and  the  plastic  mass  is  subjected 
to  considerable  pressure  and  dried.  The  lumps,  after 
being  broken  up  again  and  drained  in  a  hydroextractor, 
are  ground  and  finally  mixed  with  the  camphor  in  the 
proportion  of  one  part  of  camphor  to  two  parts  of 
pyroxylin,  though  other  proportions  also  give  good 
results. 

The  well  mixed  mass  is  then  pressed  in  order  to 
expel  any  watery  constituents  still  present;  and  further- 
more, to  bring  the  particles  of  camphor  and  pyroxylin 
into  still  more  intimate  contact  to  facilitate  the  solvent 
action  of  the  former. 

The  dried  and  pressed  mass  is  placed  in  molds  and 
given  the  desired  shape  by  the  application  of  hydraulic 
pressure,  under  heat.  On  leaving  the  press,  the  celluloid 
is  hard,  but  remains  plastic  and  can  be  re-softened  by 
warmth,  or  by  placing  it  in  boiling  water. 
2.  Cold  process  of  preparing  celluloid. 
In  operating  this  process,  the  greatest  care  must  be 
taken  on  account  of  the  great  inflammability  and  low 
boiling  point  (35-deg.  C)  of  the  ether  which  is  used  to 
dissolve  the  camphor;  thorough  ventilation  of  the  fac- 
tory rooms  is  very  essential.  The  proportions  used 
in  this  method  are  50  pounds  of  nitro-cellulose,  suffused 
with  a  mixture  of  100-parts  of  ether.  After  the  ether 
has  been  slowly  evaporated,  the  mixture  finally  becomes 
a  transparent,  sticky,  gelatinous  mass,  which  is  rolled 
between  a  pair  of  superimposed  calendering  rollers  until 
it  is  plastic.  On  exposure  to  the  air,  the  rolled  viscid 


82  MOLDED    INSULATION 

sheets  attain  a  certain  hardness.  They  are  then  warmed 
and  subjected  to  powerful  pressure.  This  is  important 
as  the  valuable  properties  of  celluloid  are  improved  in 
proportion  to  the  pressure  applied.  To  obtain  good 
celluloid  by  the  cold  ether  process  it  is  also  highly 
important  that  the  raw  material  should  be  dry  and  per- 
fectly free  from  acid,  otherwise  the  celluloid  will  be 
cloudy. 

In  another  process,  the  gun  cotton  after  being  pulped 
with  water,  is  treated  with  a  mixture  of  camphor  and 
woodspirit  (methylalcohol).  The  principle,  however,  is 
identical  with  that  of  the  other  process. 

Pure  celluloid  is  nearly  colorless.  In  thin  sheets  it 
is  as  clear  as  common  glass.  It  is  very  elastic,  trans- 
parent, tough,  and  hard.  Celluloid  has  a  faint  smell  of 
camphor  which  becomes  stronger  when  the  mass  is  rubbed. 
It  is  electrified  by  friction.  Heated  sufficiently  it  be- 
comes plastic  and  can  be  molded  into  any  shape  desired. 
On  heating  up  to  140-deg.  C.,  celluloid  loses  its  color  and 
transparency,  and  at  about  50-deg.  higher  decomposes 
Avith  the  liberation  of  pungent,  readily  inflammable 
vapors. 

Since  celluloid  softens  in  warm  water  the  molding 
process  is  greatly  facilitated  by  this  behavior.  Celluloid 
ignites  only  when  brought  in  direct  contact  with  flame 
and  then  burns  with  a  smoky  flame  giving  off  an  odor 
of  camphor.  On  blowing  out  the  flame  the  mass  con- 
tinues to  flow  and  to  give  off  thick  fumes  of  camphor. 
This  is  a  clear  proof  that  celluloid  is  not  a  chemical 
combination  of  camphor  and  gun  cotton,  since  it  is  char- 
acteristic of  chemical  reactions  that  the  substances  enter- 
ing into  combination  cease  to  exist  independently  in  the 
compound. 

Celluloid  is  insoluble  in  water  and  though  not  im- 


ORGANIC   PLASTICS  83 

mediately  attacked  by  concentrated  sulphuric  acid  it 
gradually  dissolves  therein.  A  small  piece  entirely  dis- 
appears in  about  36  hours.  Concentrated  nitric  and 
boiling  caustic  alkali  also  gradually  dissolve  it. 

The  specific  gravity  of  celluloid  varies  according 
to  the  degree  of  pressure  to  which  it  has  been  subjected 
in  the  manufacture,  the  mean  being  1.50. 

Celluloid  is  very  extensively  used  as  a  substitute  for 
horn,  tortoise  shell,  coral,  malachite,  lapis,  marble,  ebony, 
amber,  caoutchouc,  ebonite,  etc.  As  a  matter  of  fact,  there 
is  hardly  any  natural  product  which  has  not  been  imitated 
in  celluloid. 

Continuous  experimenting  and  research  is  carried  on 
in  attempts  to  render  celluloid  less  inflammable  and  to 
make  it  more  useful  as  an  electrical  insulator. 

ALBUMINOIDS— CASEIN 

The  purpose  of  the  creation  of  these  products  was 
to  obtain  a  substitute  for  celluloid  which  would  not  have 
the  poor  heat-proof  characteristics  of  the  latter.  Pro- 
ducts of  extraordinarily  fine  nature  have  been  developed, 
based  on  treating  curdled  milk  with  acetic  acid  or  other 
reagents  to  throw  down  the  casein. 

A  plastic  mass  is  thus  obtained  to  .which  organic 
or  inorganic  filling  material  is  usually  added.  It  is  then 
molded  in  heated  dies  in  a  manner  similar  to  the  ma- 
terials of  Class  "A." 

Such  products  would  not  be  stable  under  the  action 
of  moisture,  but  treatment  with  formaldehyde  renders 
this  mass  less  susceptible  to  humidity  and  other  climatic 
influences. 

These  compounds  can  be  easily  worked  with  tools  and 
stand  temperatures  of  20-deg.  to  30-deg.  higher  than  the 


84  MOLDED   INSULATION 

celluloid  compounds.  They  char  upon  the  application  of 
heat  without  inflaming. 

This  material  will,  however,  not  stand  the  continued 
action  of  water  as  well  as  the  celluloid  compounds,  but 
its  higher  heat-resisting  and  non-inflammable  qualities 
render  it  valuable  for  many  purposes. 

As  insulating  products,  these  materials  are  not  to 
be  considered  of  great  importance,  their  use  being 
practically  confined  to  the  manufacture  of  molded  articles 
for  domestic  use. 

In  all  such  compounds,  the  casein  plays  the  important 
part,  but  numerous  inventions  have  lately  been  developed 
to  partly  substitute  the  casein  by  organic  or  synthetic 
resinous  binding  products. 

While  these  newer  compounds  may  improve  the  quali- 
ties of  this  product,  they  have  not  yet  produced  materials 
of  any  great  value  for  electrical  molded  insulating  parts, 
notwithstanding  their  excellent  plastic  qualities. 


SYNTHETIC    RESINOUS    MATERIALS  85 


SYNTHETIC   RESINOUS   MATERIALS 
(Class  "G") 


In  discussing  the  hot  molded  organic  products 
(Class  "A"),  attention  has  been  called  to  their  most 
serious  defect,  namely;  their  low-melting  point  due 
to  this  characteristic  of  their  chief  binding  medium, 
namely  shellac. 

The  replacing  of  shellac  by  a  binding  medium  having 
all  the  valuable  qualities  of  this  material  without  its 
serious  defect  of  softening  at  comparatively  low  tempera- 
tures, has  been  highly  desirable. 

The  serious  interference  with  the  proper  and  reliable 
operation  of  electrical  apparatus  and  machinery  caused 
by  the  softening  or  inflaming  of  the  molded  insulating 
parts  made  of  materials  of  Class  "A"  has  caused  elec- 
trical engineers  and  designers  to  eagerly  seek  a  more 
heat  and  fire  resisting  product. 

The  materials  of  Class  "G,"  the  Phenol-Formalde- 
hyde products,  have  all  the  advantages  of  the  hot  molded 
organic  materials  (Class  "A")  and  in  addition  possess 
heat-resisting  qualities  to  a  high  degree  and  are  well 
suited  for  every  purpose  to  which  these  Class  "A"  ma- 
terials are  adapted.  Unfortunately,  their  high  manufac- 
turing cost  restricts  their  use  very  largely  to  articles 
of  electrical  insulation,  the  cost  of  which  is  of  little 
consideration  or  a  small  item  in  the  cost  of  the  apparatus. 

The  peculiar  heat-resisting  and  dielectric  properties 
of  these  products  are  due  to  the  binder,  a  synthetic 


86  MOLDED   INSULATION 

resinous  substance  obtained  by  the  chemical  reaction  of 
phenol  on  formaldehyde. 

As  early  as  1872,  such  artificial  resins  were  obtained 
and  at  various  times  since  considerable  literature  has 
been  published  and  much  research  work  undertaken  in 
endeavors  to  produce  such  synthetic  resinous  substances 
on  a  practical  commercial  basis. 

It  seems  strange  that  while  today  the  high  heat- 
resisting  properties  of  these  products  are  recognized 
as  a  vital  characteristic  advantage,  the  earlier  investiga- 
tors and  inventors  had  nothing  further  in  mind  than  to 
produce  synthetically  what  nature  had  already  given 
in  shellac. 

The  research  work  done  along  this  line  consisted 
in  combining  phenol  with  formaldehyde  by  means  of  heat, 
with  or  without  the  presence  of  acid  or  alkaline  agents, 
to  act  as  catalysers,  causing  the  mixture  to  condense. 

The  water  is  thus  eliminated  by  evaporation,  or  it 
is  otherwise  separated  from  the  viscous,  condensation 
product. 

Various  proportions  of  the  constituent  materials, 
the  kind  of  catalytic  agents  used,  the  length  of  time  of 
heating  and  temperatures,  all  affect  the  character  of  the 
resulting  compound,  which  is  first  a  viscous  liquid  and 
then  a  hard,  fusible  solid,  which  on  further  heating,  poly- 
merizes into  an  infusible  product. 

Up  to  about  six  years  ago,  such  synthetic  resinous 
bodies  were  not  valued  for  their  heat-resisting  qualities, 
that  is,  their  characteristic  of  becoming  an  infusible  sub- 
stance upon  the  further  application  of  heat;  and  they 
were  of  no  great  value  as  shellac  substitutes  in  the 
literal  significance  of  the  term  substitute,  because  of 
their  higher  cost.  Consequently,  they  were  not  much 
heard  of  outside  the  laboratory  and  in  patent  literature. 


SYNTHETIC    RESINOUS   MATERIALS          87 

The  brittleness  of  the  final  hard  product  was  another 
reason  why  their  usefulness  was  so  long  unrecognized, 
but  by  incorporating  fibrous  substances  with  these  syn- 
thetic resinous  materials  a  product  was  obtained.  Molded 
articles  made  from  this  equal  or  surpass  in  strength  every 
known  insulating  material,  with  the  exception  of  rubber 
products. 

While  the  production  of  these  phenol-formaldehyde 
compounds  has  reached  a  state  of  perfection  which  may 
reasonably  be  termed  a  scientific  as  well  as  a  commercial 
success,  very  little  is  known  of  their  exact  chemical  com- 
position. Attempts  have  been  made  to  show  a  definite 
chemical  reaction  and  a  definite  atomic  combination  be- 
tween the  constituent  elements,  but  the  various  authors 
of  such  formulae  and  theories  disagree  to  such  an  extent 
that  we  must  conclude  that  the  exact  nature  of  this 
substance  has  not  yet  been  determined,  and  await  further 
investigation  to  give  us  more  conclusive  scientific  in- 
formation. 

The  commercial  molded  insulating  products  of  this 
class  and  the  methods  employed  to  incorporate  with  them 
the  organic  or  inorganic  fibrous  filling  materials,  will 
now  be  discussed. 

One  manner  in  which  this  is  accomplished  is  by 
heating  the  mass  obtained  by  the  condensation  process 
only  to  a  point  where  it  is  plastic  when  hot,  but  hard 
when  cold.  In  this  stage  of  its  production,  it  is  ground 
to  powder  and  mixed  in  suitable  proportions  with  the 
fillers.  This  mixture  is  placed  in  heated  dies  and  held' 
under  pressure  until  the  binder  is  first  rendered  plastic 
and  then  transformed  into  the  hard  infusible  state.  The 
dies  are  then  cooled  sufficiently  to  permit  the  removal  of 
the  molded  pieces.  Such  pieces  leave  the  dies  in  a  finished 
state  exactly  as  the  shellac  compounds  do. 


88  MOLDED    INSULATION 

Generally,  these  pieces  on  the  application  of  a  flame, 
give  off  a  carbolic  acid  odor.  Some  manufacturers  try 
to  overcome  this  by  subjecting  the  pieces  to  a  further 
exposure  to  heat,  to  drive  off  these  odors. 

Another  method  of  producing  molded  articles  of 
this  class  is  to  mix  the  viscous,  condensation  mass  directly 
with  the  fillers,  heating  the  mixture  just  to  a  sufficient 
degree  to  make  it  hard  when  cold,  but  plastic  when  hot, 
grinding  it  to  a  powder  and  subjecting  this  powder  to 
the  same  treatment  as  described  above. 

It  is  therefore  seen  that  the  mixing  in  of  the  filling 
materials  and  the  molding  of  the  compound  must  be 
done  before  the  binder  reaches  its  infusible  state. 

There  are  at  the  present  day  a  great  many  patents 
covering  the  manufacture  of  these  synthetic  binders,  but 
they  are  all  based  on  the  principle  here  mentioned. 

Two  distinct  products  of  the  above  type  are  now  made 
for  electrical  purposes  with  considerable  success. 

While  the  manufacturers  claim  marked  differences 
in  their  products,  the  characteristics  of  the  binders  are 
the  same,  and  any  difference  which  exists  is  dependent 
upon  the  character  of  the  fillers. 

One  product  is  obtained  by  using  a  filler  which  is 
chiefly  an  organic  material  (wood  pulp),  while  the  other 
employs  asbestos  fibre. 

The  products  made  with  wood  pulp  have  the  ad- 
vantage of  being  more  easily  molded  and  leaving  the 
dies  with  a  more  elegant  appearance,  but  while  those 
made  with  asbestos  fibre  are  in  this  respect  somewhat 
inferior,  they  resist  heat  better,  noticeably  the  electric  arc. 

The  manufacturers  using  wood  pulp  claim  that  their 
product  is  heat-proof  to  175-deg.  C. ;  the  manufacturers 
using  asbestos  claim  250-deg.  C.  The  difference  in  the 
heat-resisting  properties  of  these  two  products  is  in  no 


SYNTHETIC    RESINOUS   MATERIALS  89 

way  dependent  on  the  binders,  it  depends  entirely  on 
the  filler. 

In  the  case  of  the  product  made  with  the  organic 
filler,  the  comparatively  low  heat-proof  quality  is  due 
to  the  nature  of  the  filling  material,  while  the  breakdown 
point  of  the  material  made  with  the  asbestos  filler  is 
the  limit  of  heat-resistance  of  the  binder. 

Both  products  are  claimed  to  be  unaffected  by 
moisture  or  water. 

Exposure  of  several  years  has  confirmed  this ;  but 
this  class  of  synthetic  binders  is  of  too  recent  introduc- 
tion to  make  a  definite  statement  as  to  their  water-resist- 
ing qualities  in  comparison  with  such  organic  binders 
as  rubber. 

The  writer  has  made  various  tests  on  both  these  pro- 
ducts, and  has  found  that  both  materials,  if  properly 
manufactured,  are  practically  unaffected  by  moisture ;  but 
the  wood-pulp  material  after  an  immersion  of  several 
months  in  water  seemed  to  be  slightly  more  affected  than 
the  materials  with  the  inorganic  filler. 

As  in  the  case  of  the  shellac  compounds,  the  more 
inorganic  filler  used  the  more  such  material  will  with- 
stand arcing;  the  more  binder  used,  the  easier  these 
pieces  are  molded  and  the  less  they  absorb  moisture. 

The  insulating  qualities  of  these  phenol-formaldehyde 
products  are  very  high,  and  they  have  found  a  ready 
market.  Another  advantage  they  possess  is  that  they  can 
be  molded  into  any  shape  with  absolute  accuracy. 


90  MOLDED    INSULATION 


FIBRE 
(Class  "H") 


Under  this  heading  we  will  discuss  those  materials 
which  have  been  known  under  this  name  from  the  earliest 
times,  and  also  a  newer  fibre  product  which  is  cemented 
by  means  of  resinous  binders. 


VULCANIZED  FIBRE 

This  material  is  prepared  by  treating  vegetable  fibres 
(paper)  with  chloride  of  zinc  or  other  metallic  chlorides, 
alkaline  compounds,  and  sulphuric  acid. 

The  fibres  are  thus  partly  dissolved  and  brought  to 
a  somewrhat  sticky  (glutinous)  condition  in  which  they 
are  subjected  to  high  pressure,  generally  in  the  form  of 
sheets  of  various  thickness. 

The  action  of  the  various  active  chemical  compounds 
used  in  the  treatment  of  the  fibre,  and  the  pressure  after- 
wards used,  render  the  product  homogeneous  and  tough; 
but  as  the  rinsing  out  of  the  excess  of  the  various  chemi- 
cals is  never  complete,  the  remaining  portions  are  the 
source  of  the  troubles  so  often  experienced  in  the  use 
of  this  material  for  electrical  insulating  purposes. 

Vulcanized  fibre  is  unaffected  by  organic  solvents. 
It  is  very  tough  and  its  property  of  being  easily  worked 
with  tools  has  made  it  an  extensively  used  product  in 
electrical  work. 


FIBRE  91 

It  does  not  burn  immediately  on  exposure  to  a  flame 
or  arc,  but  will  char  and  carry  the  flame  after  a  few 
moments  exposure  to  heat  exceeding  175-deg.  C. 

It  is  unstable  under  atmospheric  exposure,  and  warps 
and  deforms  readily.  This  inability  to  resist  water  is 
the  most  serious  drawback  to  this  product. 


FIBRE  TREATED  WITH  RESINOUS  BINDERS 

This  class  of  materials  has  come  into  favor  lately 
with  electrical  engineers,  for  it  has  the  excellent  prop- 
erties of  fibre  without  the  drawbacks  of  the  latter 's 
unstable  nature. 

These  materials  are  manufactured  by  agglomerating 
fibres  by  means  of  dissolved  resinous  substances  (such 
as  shellac  or  copal  solutions)  or  by  phenol  formaldehyde 
binders. 

The  so  agglomerated  fibrous  sheets  are  then  sub- 
jected to  pressure  under  heat  in  a  manner  similar  to 
the  manufacture  of  built-up  mica,  the  heat  causing  the 
binder  to  melt  and  thus  to  cement  the  fibrous  layers 
firmly  together. 

This  class  of  material,  when  made  with  synthetic 
resinous  binders,  is  very  stable  and  exhibits  high  dielec- 
tric and  heat-proof  qualities  and  good  mechanical  prop- 
erties. 

"When  the  binders  are  of  a  natural  resinous  nature, 
the  heat-resisting  properties  are  governed  by  the  soften- 
ing point  of  the  binder. 


92  MOLDED    INSULATION 


MOLDED  MICA 
(Class  "I") 


These  products  are  made  by  splitting  mica  into  thin 
laminae  which  are  cemented  together  by  means  of  resin- 
ous binders. 

The  so  built  up  sheets  or  forms  are  afterwards  sub- 
jected to  pressure  and  heat,  the  heat  melting  the  bind- 
ing materials,  thus  forming  a  compact  product.  Accord- 
ing to  the  nature  and  proportion  of  the  binders  used, 
these  mica  compositions  can  be  made  more  or  less  heat- 
resisting,  but  obviously  to  such  a  degree  only  as  the 
binding  material  will  withstand. 

All  attempts  so  far  to  cement  mica  in  sheets  or 
in  powdered  form  by  means  of  an  inorganic  binder  have 
failed,  but  should  these  attempts  ever  prove  successful, 
a  very  broad  field  will  be  opened  up  for  this  excellent 
insulating  material. 


PROPERTIES  93 


PROPERTIES 
LIFE 


The  first  requirement  of  a  molded  insulating  part 
is  that  it  be  stable.  That  is,  it  must  retain  its  shape 
and  physical  and  electrical  characteristics  under  service. 
It  must  not  deform  nor  disintegrate,  and  it  must  main- 
tain its  dielectric  strength. 

Neither  heat,  cold,  nor  sudden  temperature  changes, 
the  action  of  the  electrical  current,  nor  chemical  actions 
induced  by  this  current,  must  exert  any  deleterious  effect 
upon  it. 

No  material  in  use  today  perfectly  fulfills  all  of 
these  conditions. 

The  materials  which  most  nearly  meet  these  require- 
ments are  the  ceramics,  Class  "D." 

The  inorganic  compounds,  "Class  "C,"  are  also  very 
stable.  This  class  possesses  the  peculiar  characteristic 
of  improving  with  age  and  exposure  to  air  and  weather, 
in  which  important  particular  it  differs  from  porcelain, 
(which  is  inert  under  these  conditions)  and  all  other  forms 
of  molded  insulating  material  which  deteriorate  more 
or  less  with  age. 

The  bituminous,  cold  molded  materials,  Class  "B," 
while  they  do  not  meet  these  requirements  as  fully  as  the 
two  foregoing  classes,  are  still  very  durable ;  for,  during 
the  higher  temperature  treatment  to  which  they  are  sub- 


94  MOLDED    INSULATION 

jected  after  molding,  the  unstable  elements  are  either 
driven  off  or  forced  into  stable  combinations  and  ren- 
dered inert. 

The  rubber  compounds,  Class  "E":  Rubber  when 
properly  compounded  is  very  stable,  but  unfortunately 
the  increasingly  high  cost  of  the  better  grades  of  this 
valuable  substance  offers  great  temptation  to  the  manu- 
facturer and  practically  all  commercial  rubber  is  adul- 
terated with  low  grade  resinous  gums  and  other  sub- 
stitutes which  greatly  reduce  its  life  and  consequently 
its  usefulness  as  a  material  for  molded  insulating  parts. 

The  synthetic  resinous  compounds  form  a  new  class 
of  peculiar  products  which  have  been  in  use  for  a  com- 
paratively short  period  and  definite  judgment  must  be 
withheld  until  time  has  demonstrated  their  value.  The 
writer  has  seen  this  material  in  service  both  outdoors  and 
indoors,  where  it  has  seemed  to  fulfil  all  the  claims  of  its 
adherents,  but  knows  also  of  cases  where  in  outdoor  work 
it  has  not  given  satisfaction,  although  this  may  have  been 
due  to  faulty  or  careless  manufacture  and  not  to  any 
inherent  defect  in  the  material. 

It  is  the  writer's  opinion  that  the  very  broad  claims 
made  for  it  are  not  extravagant,  and  that  it  will  before 
long  be  so  fully  developed  as  to  wholly  justify  itself. 
The  shellac  compounds — Class  "A" — suffer  un- 
der the  same  disadvantages  as  the  rubber  materials. 
High  grade  shellac  compounds  are  quite  stable,  but  as 
shellac  is  comparatively  expensive,  most  of  the  materials 
of  this  class  are  adulterated,  usually  with  rosin,  which  in 
consequence  of  its  unstable  nature,  and  very  low  melting 
point,  very  seriously  affects  the  value  of  materials  of  this 
type. 

Class  "F" — The  celluloid  compounds  are  stable  at 


PROPERTIES  95 

low   temperatures,   but   due   to   their   poor  heat-resisting 
qualities    their  use  is  restricted. 

The  albuminoids  are  quite  stable  under  certain  con- 
ditions, but  in  consequence  of  their  very  hygroscopic 
nature  they  are  unsuited  for  molded  insulation. 

Class  "H"  Fibre — Ordinary  Fibre  is  falling  into 
disrepute  because  its  shape  changes  with  varying  atmos- 
pheric conditions. 

On  the  other  hand,  the  new  class  of  hardened  veget- 
able fibre  is  of  a  stable  nature.  It  is  practically  unaf- 
fected by  climatic  conditions,  although  its  use  is  not  ad- 
vised for  outdoor  insulating  work.  Owing  to  the  hygro- 
scopic nature  of  organic  fibres,  a  certain  amount  of 
moisture  is  absorbed.  It  will,  however,  retain  its  shape. 

MOLDING 

Another  fundamental  requirement  of  a  molded  in- 
sulating material  is  that  it  may  be  readily  formed  into 
such  shapes  as  the  requirements  of  the  particular  use 
to  which  it  is  to  be  put  demand. 

The  methods  employed  in  the  manufacture  of  molded 
insulation  can  be  broadly  separated  into  two  fundamental 
classes — the  cold  molding  process  and  the  hot  molding 
process. 

In  the  first  class  the  material  is  molded  in  cold 
dies  and  subjected  to  a  further  process  after  pressing. 

In  the  second  class,  the  material  is  first  rendered 
plastic  by  heat  and  then  molded  in  hot  dies,  the  articles 
being  removed  from  the  dies  when  cold  in  a  finished 
state  without  subsequent  treatment. 

The  first  method  is  employed  for  the  materials  of 
Classes  "B,"  "C"  and  "G." 


96  MOLDED    INSULATION 

The  second  method  is  employed  for  the  materials  of 
Classes  "A,"  "E,"  "F"  and  "G." 

The  materials  made  up  by  the  second  method  can 
b'e  molded  into  almost  any  shape  that  may  be  required 
and  with  great  accuracy,  as  these  materials  when  molded 
are  perfect  plastics,  and  leave  the  dies  in  a  finished  con- 
dition. 

The  fact  that  the  materials  made  by  the  first  method 
have  to  be  treated  after  pressing  has  been  responsible  for 
a  great  deal  of  inaccuracy  of  dimensions  in  cold  molded 
insulating  parts.  The  materials  used  in  the  first  method 
are,  generally  speaking,  not  so  easily  molded  into  com- 
plicated shapes,  nor  with  such  a  nice  degree  of  accuracy, 
but  considerable  progress  has  been  made  in  the  last  few 
years  in  this  particular  branch  of  insulating  manufacture, 
and  parts  can  now  be  obtained  which  meet  all  reasonable 
requirements. 

Attention  shquld  be  called  here  to  the  peculiarity  of 
the  materials  of  Class  "B"  not  being  suitable  for  molding 
into  flat  plates  or  parts  of  large  size.  On  the  other 
hand,  the  materials  of  Class  "C,"  are  particularly  adapt- 
able for  such  purposes. 

Materials  in  Class  "D"  are  liable  to  a  shrinkage  as 
high  as  15%  in  their  subsequent  treatment  (firing).  This 
makes  it  difficult  to  control  with  accuracy  the  dimensions 
of  the  finished  piece,  and  it  has  become  a  custom  of  the 
trade  using  porcelain  to  allow  a  variation  of  .015  per  inch 
or  more  in  parts  made  of  this  material. 

Some  manufacturers  of  materials  of  Classes  "B"  and 
"C". claim  that  they  can  mold  true  to  size,  while  others 
require  the  acceptance  of  a  variation  not  exceeding  .010 
of  an  inch,  especially  in  pieces  of  complicated  form,  but 
it  would  be  advisable  for  designers  of  parts  to  be  made 
of  cold  molded  materials  to  bear  in  mind  that  all  such 


PROPERTIES  97 

materials  are  apt  to  vary  slightly  from  the  drawings 
and  not  to  originate  such  combinations  of  insulating 
material  and  metallic  parts  as  may  be  unfavorably  af- 
fected by  a  variation  of  a  few  thousandths  of  an  inch. 

For  pieces  in  which  no  variations  can  be  allowed 
and  where  extreme  accuracy  and  perfect  finish  are  re- 
quired, materials  of  classes  "A,"  "E,"  or  "G"  are 
to  be  preferred,  provided  other  conditions  permit  their 
use. 

Practically  all  molded  insulating  materials  except 
those  of  Class  "D"  can  be  manufactured  with  metal 
parts  imbedded  in  them. 

The  practice  of  molding  in  metal  parts  has  become 
very  extensive  and  has  been  a  large  factor  in  the  suc- 
cessful introduction  of  molded  insulation,  as  it  has  elimi- 
nated the  process  of  inserting  these  parts  in  the  shop, 
which  process  is  often  expensive  and  unsatisfactory. 

On  the  other  hand,  such  excellent  results  have  been 
obtained  by  this  process  of  incorporating  metallic  in- 
serts in  molded  parts  that  some  designers  have  become 
over  enthusiastic  in  regard  to  this  feature,  and  expect 
too  much  of  the  molded  insulation  manufacturers,  espe- 
cially in  pieces  of  complicated  design,  and  they  would 
do  well  when  designing  new  combinations  to  consult 
with  the  manufacturer  from  whom  they  expect  to  pur- 
chase before  going  too  far  with  their  specifications  and 
drawings. 

The  materials  of  Class  "H"  are  not  strictly  molded 
materials,  but  are  furnished  in  sheets,  tubes  and  rods. 

PUNCTURE  TEST 

The  insulating  value  of  molded  materials  is  usually 
determined  by  puncture  tests. 


98  MOLDED    INSULATION 

As  this  treatise  will  not  discuss  insulation  for  high 
tension  work,  and  has  only  to  consider  voltages  below 
one  thousand,  the  materials  of  all  the  different  classes 
herein  enumerated  can  be  considered  as  chosen  for  the 
particular  conditions,  and  the  thickness  of  the  insulating 
part  is  designed  to  correspond  to  the  insulating  properties 
of  the  material  selected. 

The  insulating  properties  of  porcelain  or  other  cer- 
amics vary  according  to  the  properties  of  the  chemical 
components  of  the  product. 

The  insulating  properties  of  the  cold  molded  inor- 
ganic materials  Class  "C"  vary  not  only  according  to 
their  composition,  but  to  the  treatment  they  receive  in 
the  various  stages  of  their  manufacture. 

Class  "B" — In  the  cold  molded  organic  materials, 
the  mixture  again  plays  an  important  part,  but  the 
amount  of  pressure  and  conditions  under  which  the  piece 
is  subjected  to  this  pressure  determine  to  a  very  great 
extent  the  nature  and  value  of  these  products. 

Classes    "A"    and    "E"— The  Shellac    and   Rubber 

Compounds.     The  variation  in  the  insulating  properties 

of  these  materials  depends  almost  entirely  on  the  com- 
pounding of  the  products. 

The  amount  of  pressure  employed  in  molding  is  not 
of  great  importance,  provided  sufficient  pressure  is  used 
to  thoroughly  weld  the  ingredients. 

Class  "F" — The  organic  plastics  are  uniformly  of 
high  dielectric  strength.  They  are  dense,  homogeneous 
masses  composed  of  ingredients  of  high  insulating  value 
and  contain  no  fillers  to  render  them  porous,  or  to  reduce 
by  their  lower  insulating  value  the  point  at  which  these 
materials  puncture. 


PROPERTIES  99 

Class  "G"-  —  The  synthetic  resinous  materials  vary  in 
dielectric  strength  somewhat  according  to  the  nature  of 
the  synthetic  binder.  These  binders  as  produced  today 
do  not  differ  greatly  from  each  other  in  respect  to  their 
dielectric  strength,  hence,  the  value  of  materials  made 
with  them  as  the  important  ingredient,  depends  princi- 
pally upon  the  nature  of  the  fillers  entering  into  their 
manufacture. 

Class  "H" — Fibre  like  the  organic  plastics  is  of  a 
homogeneous  nature  and  its  insulating  value  doe  not 
vary  greatly,  but  is  somewhat  dependent  upon  the  physi- 
cal treatment  and  seasoning  it  undergoes  in  its  manu- 
facture. 

The  newer  materials  of  this  class,  i.e.,  those  formed 
of  thin  sheets  impregnated  by  and  cemented  together 
with  organic  or  synthetic  resinous  materials,  depend  very 
largely  on  the  latter  for  their  insulating  value,  but  they 
are  also  affected  to  a  considerable  degree  by  the  tempera- 
ture and  pressure  to  which  they  are  subjected  during 
their  manufacture. 

Class  "I"-— The  high  insulating  value  of  molded  mica 
depends  almost  entirely  on  the  great  dielectric  strength 
of  the  mica,  the  other  ingredients  being  employed  merely 
to  cement  and  hold  the  mica  flakes  together. 

MECHANICAL  STRENGTH 

One  quality  of  prime  importance  which  a  molded 
insulating  piece  must  possess  is  mechanical  strength. 

Years  ago  when  porcelain,  fibre,  hard  rubber  and 
wood  were  the  standard  insulating  materials,  fibre  was 
generally  employed  for  those  parts  which  were  subjected 
to  unusual  stress. 


100  MOLDED   INSULATION 

As  long  as  fibre,  wood,  or  a  good  quality  of  hard 
rubber  was  used,  metal  parts  were  often  embedded  in,  or 
fastened  to  the  insulating  parts  by  drilling  and  then 
threading  and  screwing,  or  by  simply  punching  and 
riveting. 

The  strength,  toughness  and  resilient  properties  of 
those  materials  were  such  that  these  methods  of  manu- 
facture and  assembling  were  not  objectionable.  Design- 
ing and  manufacturing  departments  became  accustomed 
to  this  treatment,  and  when  the  various  new  insulating 
materials  were  introduced  they  frequently  entirely  over- 
looked the  fact  that  these  newer  substances  might  not 
possess  the  same  mechanical  characteristics  as  those  with 
which  they  were  familiar;  and  the  old  processes  of  drill- 
ing, riveting,  etc.  were  attempted  with  unsatisfactory 
results.  The  usual  consequence  then  was  that  these 
materials  were  condemned  by  the  workmen  because  they 
were  different  from  those  to  which  they  had  become 
accustomed. 

This  condition  of  affairs,  more  than  anything  else, 
retarded  the  introduction  of  molded  insulating  parts, 
and  gave  manufacturers  of  these  parts  untold  trouble 
and  expense,  until  it  was  demonstrated,  that  their  pro- 
ducts possessed  advantages  sufficiently  valuable  to  more 
than  compensate  for  the  apparent  defect  of  requiring 
somewhat  different  treatment  and  handling. 

Fibre  is  still  quite  extensively  employed  in  many 
shops,  particularly  for  experimental  work,  and  where  on 
account  of  the  small  number  of  pieces  required,  the  ex- 
pense of  a  die  is  a  considerable  factor  in  the  cost  per 
piece.  However,  even  the  newer  fibre  materials  cannot 
compete  with  molded  insulating  parts  if  used  in  large 
quantities,  and  materials  of  this  type  are  destined  to  con- 
stantly decrease  in  popularity,  except  for  experimental 


PROPERTIES  101 

and   special  work  or  where   great  flexibility,   resiliency 
and  mechanical  strength  are  of  first  importance. 

The  molded  insulation  products  which  have  come 
nearest  to  fibre  for  strength  and  toughness  are  those  of 
Class  "E,"  the  rubber  compounds,  and  more  lately  those 
of  Class  "G,"  the  synthetic  resinous  materials.  Some- 
of  the  materials  of  both  of  these  classes  possess  excellent 
mechanical  strength  and  are  equal,  if  not  superior,  in 
this  respect  to  any. 

Porcelain  is  one  of  the  very  best  insulating  ma- 
terials we  have,  and  wherever  its  brittleness  is  not  a 
serious  drawback,  its  use  is  recommended,  particularly 
on  account  of  its  low  cost.  Contrary  to  general  opinion, 
its  tensile  strength  is  high,  but  unfortunately  its  elas- 
ticity is  very  low  and  consequently  it  will  not  withstand 
shock,  and  should  not  be  employed  where  it  will  be  sub- 
jected to  sudden  strains  or  excessive  vibration. 

Materials,  which  have  successfully  competed  with  and 
to  a  large  measure  have  already  replaced  porcelain,  are 
those  of  Classes  "B"  and  "C,"  the  organic  and  inorganic 
cold  molded  materials,  and  parts  made  of  these  materials 
when  properly  designed  and  used,  give  excellent  results 
because  they  are  less  brittle  and  more  resilient. 

Before  the  introduction  of  the  cold  molded  ma- 
terials "B"  and  "C,"  the  hot  molded  organic  materials 
of  class  "A"  seemed  destined  to  surpass  porcelain  for 
a  great  variety  of  purposes,  on  account  of  their  superior 
mechanical  strength,  but  owing  to  their  poor  heat-resist- 
ing properties,  they  themselves  have  been  in  turn  super- 
seded by  the  cold  molded  materials  because  of  the  better 
heat-resisting  qualities  of  the  latter,  there  being  as  a 
rule  no  characteristic  difference  in  the  mechanical 
strength  of  materials  of  Classes  "A"  and  "B."  The 


102  MOLDED    INSULATION 

inorganic  materials  of  Class  "C"  possess  a  greater 
mechanical  strength  than  the  products  of  Classes  "A" 
and  "B,"  although  they  are  not  quite  as  strong  as  those 
of  Classes  "E"  and  "G." 

The  materials  of  Class  "F"  are  fairly  strong,  but 
they  are  seldom  chosen  for  this  reason.  They  are  usually 
employed  because  of  their  ornamental  appearance. 

No  matter  what  insulating  material  is  selected,  manu- 
facturers should  always  bear  in  mind  that  it  is  advisable 
to  design  electrical  apparatus  so  that  the  insulating  parts 
may  fulfil  their  primary  function  as  an  insulator,  with- 
out being  subjected  to  undue  mechanical  stress,  and  that 
this  stress  should  be  put  upon  parts  and  materials  which 
by  their  very  nature,  are  better  able  to  sustain  it. 


WEATHERPROOF  QUALITIES 

The  ability  to  resist  the  effects  of  moisture  is  a  very 
essential  requirement  of  a  molded  insulating  material. 

No  matter  how  good  in  all  other  respects  a  molded 
insulating  material  may  be,  if  it  is  affected  by  moisture 
to  such  a  degree  that  it  either  deforms,  disintegrates  or 
loses  its  dielectric  properties  to  such  an  extent  as  to 
cause  short  circuit,  it  is  useless. 

No  insulating  material  is  entirely  unaffected  by 
moisture  or  water.  A  material  is  said  to  be  "non- 
hygroscopic"  when  it  is  affected  by  water  only  to  so  slight 
a  degree  that  this  defect  can  be  safely  disregarded. 

Moisture  has  no  effect  on  materials  of  Class  "D," 
although  in  their  uriglazed  condition  they  absorb  water 
to  a  certain  extent,  but  this  is  entirely  overcome  by  the 
glazing  process.  Porcelain  may,  therefore,  be  considered 
as  the  best  material  in  this  regard. 


PROPERTIES  103 

Class  "C"  (Inorganic  cold  molded  materials).  Moist- 
ure has  no  deteriorating  effect  on  this  class  of  products, 
but  in  their  untreated  condition,  they  absorb  moisture 
to  such  an  extent  as  to  make  them  unsuited  for  pur- 
poses where  they  come  in  continuous  contact  with  water. 
In  their  treated  condition,  however,  the  absorption  of 
moisture  is  reduced  to  a  point  where  it  does  not  materially 
affect  their  insulating  properties,  and  they  have  been 
used  with  success  for  the  last  10  years  for  outdoor 
insulating  purposes. 

Class  "B" — In  the  organic  cold  molded  materials, 
the  filler  is  so  thoroughly  saturated  with  the  waterproof 
binder  that  the  absorption  of  moisture  is  so  slight  as 
to  be  negligible,  and  these  materials  may  properly  be 
classified  as  waterproof.  The  writer  knows  of  many 
instances  where  these  products  have  been  in  continuous 
outdoor  service  for  more  than  ten  years  without  show- 
ing the  slightest  deterioration. 

Class  "A"  (The  organic  hot  molded  materials). 
When  high  class  gums  are  employed  in  the  manufacture 
of  the  binder,  these  materials  are  absolutely  waterproof. 

Class  "E"-  —  The  hard  rubber  compounds  are 
thoroughly  waterproof,  although  when  made  for  high 
heat-resistance  and  containing  an  excess  of  asbestos  fibre, 
they  will  absorb  water  to  some  degree.  This,  however, 
has  no  serious  effect,  except  that  it  lowers  somewhat 
the  dielectric  strength. 

.  Class  "G" — The  synthetic  resinous  products  possess 
the  same  excellent  waterproof  qualities  as  the  properly 
made  materials  of  Class  "A" — at  least,  the  five  years 
during  which  these  materials  have  been  upon  the  market 
has  so  far  justified  such  an  opinion. 


104  MOLDED    INSULATION 

Class  "F" — The  celluloid  products  are  absolutely 
waterproof,  while  the  casein  compositions  are  not  suited 
to  use  where  they  will  be  exposed  to  moisture. 

Class  "H" — Fibre  has  fallen  into  disrepute  because 
of  its  very  hygroscopic  nature,  but  the  newer  class  of 
this  material  is  expected  to  gain  favor  because  it  does 
not  exhibit  this  disadvantage. 


HEATPROOF  QUALITIES 

During  the  last  ten  years  operating  conditions  and 
the  development  in  all  electrical  lines  have  made  in- 
creased demands  upon  the  heatproof  qualities  of  electrical 
insulating  parts,  and  the  underwriters  requirements  in 
this  particular,  have  become  stricter  and  stricter,  until 
today  the  heat-resisting  properties  of  an  electrical  in- 
sulating part  is  one  of  the  most  important  factors  in  the 
choice  of  such  materials. 

The  term  fireproof  is  frequently  used  in  describing 
molded  electrical  insulation,  but  in  a  strict  scientific 
sense  nothing  is  fireproof,  and  in  a  commercial  or  prac- 
tical sense,  insulation  is  rarely  required  to  be  fireproof. 
The  term  heat-resistant  or  heatproof  is  employed  to 
those  materials  which  do  not  soften  readily  or  at  all 
under  excessive  heat;  or  which  do  not  burn  or  char 
upon  contact  with  flame  or  the  electric  arc,  or  will 
cease  to  burn  as  soon  as  the  burning  agent  is  withdrawn. 

The  most  heatproof  materials  obtainable  today  are 
Ihe  Ceramics,  the  best  known  and  most  widely  used 
product  of  this  class  being  porcelain,  and  whenever  con- 
ditions permit  its  use,  it  is  to  be  recommended.  It  is, 
however,  liable  to  crack  under  sudden  temperature 


PROPERTIES  105 

changes  of  wide  range.  Under  such  conditions,  the 
lavite  products  are  preferable,  as  they  will  withstand 
sudden  and  even  violent  variations  of  temperature  some- 
what better. 

Where,  for  mechanical  or  other  reasons,  porcelain 
is  not  suitable,  the  choice  lies  between  the  organic  cold 
molded  materials,  the  inorganic  cold  molded  materials 
or  the  synthetic  resinous  products.  All  these  materials 
may  be  considered  heatproof  in  that  they  will  not  soften 
or  be  otherwise  disadvantageously  affected  when  continu- 
ously subjected  to  a  temperature  of  100-deg.  C.,  which 
is  the  usual  maximum  working  temperature  of  electrical 
machinery. 

The  hot  molded  organic  materials  (Class  "A"),  the 
rubber  compounds  (Class  "E")  and  the  organic  plastics 
(Class  "F")  are  all  seriously  affected  by  the  continuous 
application  of  such  a  temperature. 

Of  the  three  Classes  "B,"  "C"  and  "G,"  the  syn- 
thetic resinous  materials  (Class  "G")  are  the  strongest, 
and  because  of  their  excellent  molding  qualities  and  their 
neat  appearance,  they  are  to  be  preferred  where  cost 
is  a  secondary  consideration.  These  materials  will  with- 
stand continuously  a  temperature  of  from  150-deg.  C. 
to  250-deg.  C.,  depending  on  the  nature  and  percentage 
of  the  filling  medium  employed. 

For  most  purposes,  however,  such  as  in  the  construc- 
tion of  lighting  fixtures  and  electrical  apparatus  of  all 
kinds  where  the  .cost  of  the  insulating  parts  is  not  of 
minor  or  negligible  importance,  and  heatproof  qualities 
are  essential,  the  cold  molded  materials  (Classes  "B"  and 
"C")  are  more  suitable. 

It  is  not  advisable  to  employ  the  organic  cold  molded 
materials  (Class  "B")  for  continuous  temperatures  above 
300-deg.  C.,  while  the  inorganic  cold  molded  materials 


106  MOLDED   INSULATION 

(Class  "C")  are  perfectly  reliable  under  the  continuous 
action  of  temperatures  up  to  900  deg.  C. 

If,  in  the  manufacture  of  materials  of  Classes  "B" 
and  "G,"  the  ingredients  are  proportioned  so  that  an 
inorganic  filler  is  thoroughly  and  intimately  inter- 
mingled with  a  proper  minimum  quantity  of  the  organic 
binder,  products  can  be  obtained  upon  which  the  elec- 
tric arc  has  but  little  effect. 

In  general,  however,  it  is  advisable  to  manufacture 
arc  deflectors  and  all  parts  which  are  subjected  to  con- 
stant arcing  and  similar  conditions,  of  the  inorganic  cold 
molded  materials,  as  their  inorganic  nature  precludes  all 
possibility  of  softening  or  charring. 

While  these  materials  are  unaffected  by  arcing  or 
momentary  temperatures  of  1500-deg.  C.,  they  should 
be  used  with  caution  for  service  where  they  will  be  sub- 
jected to  continuous  temperatures  of  over  900-deg.  C., 
as  may  be  the  case  in  resistance  insulators,  for  instance. 
Although  materials  of  this  type  Class  "C"  are  in  use 
today  for  such  purposes  and  are  apparently  giving  satis- 
faction, nevertheless,  it  must  be  borne  in  mind  that 
very  high  temperatures  above  900-deg.  C.  sustained  for 
too  long  a  time  are  apt  to  split  up  the  water  of  constitu- 
tion, and  thereby  affect  the  nature  of  these  materials. 
But  under  these  conditions,  some  of  the  constituents  will 
fuse,  and  this  fusion,  if  only  partial,  will  offset  the  loss 
of  mechanical  strength,  due  to  the  dissociation  of  the 
water. 

However,  it  has  been  amply  demonstrated  that  the 
inorganic  cold  molded  materials  are  inert  under  con- 
tinuous temperatures  of  nearly  900-deg.  C.,  sustained 
for  long  periods  of  time. 

The  materials  of  Class  "II,"  fibre,  should  not  be 
employed  where  they  will  be  subjected  to  the  influences 


PROPERTIES  107 

of  the  arc  or  continuous  temperatures  above  150-deg.  C. 
The  vulcanized  products  of  this  class  are  apt  to  warp  at 
100-deg.  C. 

The  organic  hot  molded  materials  (Class  "A")  will 
not  withstand  the  electric  arc,  and  they  should  not  be 
exposed  to  continuous  temperatures  above  SO-deg.  C., 
owing  to  the  low  melting  point  of  the  binders  employed. 

The  heat-resisting  properties  of  built-up  mica  (Class 
"I")  are  limited  by  the  melting  point  of  the  shellac,  and 
unless  the  sheets  of  mica  are  confined  and  positioned 
by  some  mechanical  means,  these  products  will  not  stand 
temperatures  in  excess  of  100-deg.  C. 


RESISTANCE  TO  CHEMICAL  ACTION 

Materials  intended  to  withstand  the  continued  action 
of  acids  or  alkalies  must  be  carefully  chosen.  While  most 
insulating  compounds  will  resist  these  actions  to  a  greater 
or  lesser  degree,  few  of  them  are  proof  against  acids 
or  alkalies  for  any  great  period  of  time. 

The  only  materials  which  can  be  safely  employed 
for  this  purpose  are  those  of  Class  "D,"  the  Ceramics, 
and  to  a  certain  extent  the  products  of  Class  "E,"  the 
especially  compounded  hard  rubber  materials.  All  other 
materials  must  be  regarded  with  suspicion  for  such  work. 

MACHINING  OF  MOLDED  PIECES 

One  of  the  chief  advantages  of  molded  insulation 
is  that  it  can  be  delivered  to  the  user  in  an  absolutely 
finished  state,  and  it  is  not  intended  to  be  worked  by 
means  of  tools.  However,  with  the  exception  of  Class 
"D,"  all  these  materials  can  be  worked  with  more  or 


108  MOLDED    INSULATION 

less  satisfaction,  although  it  is  not  advisable  to  attempt 
it,  but  rather  to  design  the  parts  so  that  no  machining 
will  be  necessary. 

Class  "H,"  however,  may  be  worked  with  consider- 
able facility  and  this  is  the  chief  reason  why  these  ma- 
terials continue  to  be  used  to  a  limited  extent  for  almost 
every  electrical  application. 


COLOR  AND  APPEARANCE 

The  color  and  appearance  of  molded  insulating  parts, 
while  not  usually  of  primary  importance,  are  sometimes 
deciding  factors. 

The  color  of  the  various  insulating  materials  is  gen- 
erally dependent  upon  the  colors  of  their  principal  in- 
gredients, and  only  in  special  instances  do  coloring 
materials  play  an  important  part. 

Materials  of  Class  "D,"  for  instance,  are  usually 
white,  but  in  some  cases  the  glazing  is  done  in  various 
colors. 

In  materials  of  Class  "B"  the  color  is  usually  black 
and  depends  upon  the  ingredient  substances  which  cannot 
be  changed.  This  material  can  be  furnished  with  a  very 
high  finish. 

In  materials  of  Class  "C"  the  color  is  usually  white 
or  black,  but  these  materials  can  be  furnished  in  various 
colors.  The  materials  of  this  class  present  a  smooth, 
close-grained,  attractive,  appearance,  but  do  not  take  a 
high  polish. 

The  materials  of  Class  "A"  are  naturally  black  or 
brown,  but  by  the  introduction  of  coloring  matter,  they 
can  be  made  in  a  wide  range  of  colors.  Materials  of 
this  class  usually  leave  the  die  with  a  high  polish. 


PROPERTIES  109 

The  natural  color  of  materials  of  Class  "G"  is  a 
reddish  brown,  but  they  are  very  often  made  in  black  and 
can  be  produced  in  various  colors  by  the  addition  of 
coloring  matter.  Their  appearance  is  the  same  as  is 
Class  "A." 

Class  "E" — The  asbestos-rubber  compounds  are 
usually  furnished  in  their  natural  gray-brown  and  the 
hard  rubber  in  black  color,  but  they  can  be  made  in  a 
variety  of  colors.  Most  of  the  hard  rubber  compounds 
take  a  very  high  polish. 

The  materials  of  Class  "F"  are  particularly  adapted 
to  coloring  and  can  be  furnished  in  a  very  wide 
range  of  colors  and  finishes,  and  for  this  reason  are 
occassionally  used  on  account  of  their  appearance. 

Materials  of  Class  "H"  are  furnished  in  a  variety 
of  colors,  but  are  usually  gray,  black  or  red. 

AVhere  an  ornamental  appearance  is  essential  and 
a  high  polish  is  required,  designers  should  remember 
that  the  quality  of  the  surface  of  the  products  of  Classes 
"A,"  "E,"  "F"  and  "G"  is  due  to  the  method  of  manu- 
facture and  the  character  of  the  material,  and  that  they 
leave  the  die  with  a  high  polish,  or  that  same  can  be 
obtained  by  a  simple  buffing  process. 

On  the  other  hand,  the  products  of  Classes  "B" 
and  "C"  while  they  come  from  the  molds  with  a  smooth 
and  continuous  surface,  present  a  flat  and  lusterless  ap- 
pearance, and  in  order  to  give  them  a  high  polish  they 
must  be  ground  on  fine  .abrasive  wheels  or  carborundum 
or  like  material,  and  then  buffed.  It  is  self-evident  that 
such  treatment  cannot  be  satisfactorily  applied  to  parts 
having  small  or  intricate  projections  and  depressions,  or 
to  parts  of  irregular  and  complicated  shape. 


110  MOLDED    INSULATION 


MOLDS  AND  DIES 


In  the  molded  insulating  trade  these  terms  are 
synonymous. 

Most  electrical  engineers  are  familiar  with  some 
methods  employed  in  the  construction  and  operation  of 
the  molds  in  general  use  in  the  manufacture  of  insulating 
parts.  The  molds  play  a  very  vital  part  in  such  manu- 
facture and  are  often  the  cause  of  serious  difficulty  to 
the  manufacturer,  and  consequent  misunderstanding  be- 
tween him  and  his  customer.  The  author  will  as  briefly 
and  comprehensively  as  possible  sketch  the  more  impor- 
tant factors  in  their  construction  and  use,  to  enable  the 
user,  through  a  better  understanding  of  their  operation, 
to  avoid  those  elements  of  design  which  tend  to  compli- 
cate manufacturing  operations.  This  knowledge  will 
facilitate  the  selection  of  forms  for  his  insulating  parts 
which,  while  rendering  them  no  less  effective  for  his  pur- 
poses, will  enable  the  manufacturer  to  produce  pieces  of 
minimum  cost,  maximum  efficiency  and  neat  appearance. 

Frequently  designers,  when  bringing  out  new  forms, 
insist  on  having  dies  of  the  cheapest  construction  made 
in  order  to  get  out  a  few  sample  pieces.  This  results  in 
serious  trouble  for  the  manufacturer,  and  dissatisfaction 
for  the  customer  until  a  proper  mold  is  substituted. 

This  is  especially  true  when  the  form  of  the  piece 
is  in  any  way  complicated  by  holes,  projections,  or  irregu- 
lar surfaces,  and  unless  the  molds  are  made  of  the  very 


MOLDS    AND    DIES  111 

best  steel,  and  all  the  parts  come,  together  with  a  per- 
fect fit,  the  molded  pieces  will  be  more  or  less  misshapen 
and  have  burrs  or  fins  on  their  edges.  These  imperfec- 
tions are  a  frequent  cause  of  complaint.  It  is,  therefore, 
very  important  to  have  the  molds  of  such  quality  that 
they  will  wear  for  as  long  a  time  as  possible  without 
producing  pieces  with  these  defects.  All  dies  will  eventu- 
ally wear  out,  and  the  only  remedy  then  is  to  replace 
the  worn  parts  or  make  complete  new  dies. 

The  form  of  the  piece  and  the  character  of  the 
material  to  be  molded  play  an  important  part  in  this 
particular,  and  a  mold  may  show  more  wear  after  a  run 
of  10,000  pieces  of  one  material  than  it  would  after 
turning  out  100,000  pieces  of  another  material. 


TYPES  OF  MOLDS  OR  DIES  USED  IN  THE  MANU- 
FACTURE OF  MOLDED  INSULATION 

There  are  two  different  classes  of  dies  in  general 
use.  They  are  known  as  " OPEN  DIES"  and  "CLOSED 
DIES." 

The  term  "OPEN"  is  applied  to  that  class  of  dies 
or  molds  which  are  composed  essentially  of  two  flat 
pieces  in  one  or  both  of  which  a  recess  is  provided  to 
hold  the  material  to  be  molded.  In  operation,  these 
plates  come  together  at  a  cutting  edge  which  chops  off 
the  excess  of  material  which  has  been  squeezed  out  of 
the  recess  containing  the  molded  part. 

The  term  "CLOSED"  is  applied  to  that  class  of 
dies  or  molds  which  are  composed  essentially  of  a  plunger 
and  a  box.  In  operation,  just  enough  material  to  form 
the  part  is  placed  in  the  box;  the  plunger  then  enters 
the  box  and  forces  the  material  to  all  parts  of  the  mold. 


112 


MOLDED    INSULATION 


In  practice  these  dies  are  made  with  two  plungers;  the 
upper  plunger,  which,  generally  speaking,  does  the  com- 
pressing; and  the  lower  plunger,  which  forms  the  bottom 
of  the  mold,  and  which,  after  the  piece  is  formed,  raises 
to  push  the  piece  from  the  mold. 

Both  "OPEN"  and  "CLOSED"  dies  are  in  general 
use  for  the  manufacture  of  hot  molded  materials,  while 
only  closed  dies  are  employed  in  the  manufacture  of  cold 
molded  products. 


FIG.    1 


Figure  I  represents  an  open  die,  such  as  is  used  in 
the  manufacture  of  materials  of  Classes  "A,"  "E,"  "F" 
and  "G,"  when  such  materials  are  prepared  in  sheet  or 
cake  form  and  placed  between  the  compressing  plates  in 
a  warm  or  plastic  condition. 

This  die,  which  is  intended  to  produce  a  disc  or 
short  cylinder  having  parallel  sides,  is  made  in  three 
parts,  the  Bottom  Plate  "A,"  to  which  is  screwed  or 
otherwise  fastened  the  middle  plate  "D,"  containing 


MOLDS   AND    DIES 


113 


the  opening  "C,"  in  which  the  piece  is  to  be  formed, 
and  the  top  Plate  "B,"  which  closes  the  die,  guided 
by  the  pins  "E." 

In  operation  the  die  is  heated;  an  excess  of  material 
is  placed  in  the  cavity  "C;"  the  die  is  closed;  the 
Cutting  Edge  "F"  cuts  off  the  surplus  material,  which 
has  been  squeezed  into  the  depression  "G"  formed  to 
receive  it.  The  die  is  then  cooled  and  opened;  the  plate 
"D"  is  released  from  the  plate  "A,1'  and  the  finished 
piece  is  pushed  out  by  the  fingers  or  other  means. 


FIG.   2 


If  the  sides  of  the  piece  instead  of  being  straight 
are  tapered,  a  simpler  form  of  mold  shown  in  Figure  2 
can  be  used. 

In  this  case,  the  die  can  be  made  in  two  parts,  and 
after  the  piece  is  formed  and  the  die  cooled,  the  piece, 
due  to  its  tapered  form  and  the  shrinkage  incidental  to 
cooling,  can  be  readily  removed  by  simply  inverting  the 
die  and  rapping  it  till  the  piece  falls  out. 


114 


MOLDED    INSULATION 


FIG.  3 


In  Figure  3  is  shown  a  closed  die,  such  as  is  used  in 
the  molding  of  materials  in  a  heated  state  and  comprises 
a  Box  "D,"  an  Upper  Piston  "C,"  and  a  Lower  Piston 
"B,"  having  between  them  a  cavity  "A"  in  which  the 
piece  is  formed.  It  will  be  noticed  that  the  upper  piston 
is  longer  than  the  lower  one. 

In  operation  the  Box  "D,"  with  the  Lower  Piston  "B" 
is  placed  upon  a  heated  press  table  and  the  material  to 
be  pressed  is  placed  in  the  Cavity  "A,"  see  Figure  4. 
Before  pressing,  this  material  occupies  a  volume  con- 
siderably greater  than  the  volume  of  the  finished  piece, 
and  for  this  reason  the  Top  Piston  must  be  longer 
than  the  Bottom  Piston,  since  it  must  travel  into 


MOLDS   AND    DIES 


115 


FIG.  4 


the  box  a   sufficient   distance  to   compress  the  material 
to  be  molded  to  the  required  density. 

The  Top  Piston  is  now  placed  in  the  Box  and  the 
Upper  Platen  of  the  press,  which  is  also  heated,  is 
brought  down  by  hydraulic  or  other  pressure  on  the 
Piston  "C"  until  its  top  surface  is  'flush  with  the  top 
of  the  Box  "D."  The  die  is  now  held  between  the 
heated  plates  of  the  press  until  the  material  in  the 
Cavity  "A"  is  melted.  The  steam  is  then  shut  off  and 
cold  water  is  run  through  the  plates  of  the  press  until 
the  material  in  Cavity  "A"  is  sufficiently  cooled  to 
render  it  hard  enough  to  permit  of  its  removal  from  the 
mold. 


116  MOLDED   INSULATION 

Sometimes  the  walls  of  the  Box  "D"  are  provided 
with  channels  through  which  the  steam  and  water  are 
run  to  expedite  the  molding  process. 

In  practice,  steam  is  kept  on  the  press  plates  and 
molds  just  a  sufficient  length  of  time  to  properly  melt 
the  material  to  be  molded,  and  the  water  is  run  through 
only  long  enough  to  permit  of  the  ready  removal  of 
the  finished  piece,  as  the  time  consumed  in  these  opera- 
tions determines  the  output  of  the  press,  and  so  directly 
affects  the  cost  of  the  piece.  In  making  parts,  such  as 
bushings  and  other  pieces  having  holes  in  them,  which 
are  formed  by  pins  incorporated  in  the  mold,  the  piece 
must  be  removed  from  the  die  before  the  shrinkage 
has  progressed  to  a  point  where  the  material  would  seize 
upon  the  pins  and  thus  prevent  its  easy  removal  from  the 
mold. 

It  is  necessary  that  the  Pistons  "B"  and  "C"  should 
be  a  nice  fit  in  the  Box  "D"  in  order  that  the  pieces  may 
come  from  the  dies  without  burrs,  which  would  otherwise 
form  at  "E,"  Figure  3.  This  is  particularly  true  in  the 
case  of  materials  of  Classes  "A,"  "E,"  "F"  and  "G?" 
which  come  from  the  molds  in  a  finished  and  highly 
polished  condition,  and  are  not  subjected  to  any  further 
finishing  treatment. 

It  is  obvious,  however,  that  constant  use  will  eventu- 
ally cause  the  box  and  plunger  to  wear,  when  the  mold 
will  necessarily  produce  defective  pieces. 

This  type  of  die  may  be  used  for  molding  any  class 
of  material,  but  is  usually  employed  in  the  hot  molding 
of  such  materials  as  those  of  Classes  "A,"  "E,"  "F" 
and  "G." 

Figure  5  shows  a  die  of  the  type  used  in  the  manu- 
facture of  cold  molded  materials,  such  as  those  of  Classes 
"B,"  "C"  and  "D."  This  die  embodies  the  same  gen- 


MOLDS   AND    DIES 


117 


FIG,  5 

eral  principles  as  those  shown  in  Figure  3,  but  in  this 
case,  the  Upper  Piston  "C"  is  attached  to  the  Plate 
"H,"  which  in  turn  is  attached  to  the  upper  platen  of 
the  press.  The  Box  "D"  is  attached  to  a  Plate  "K," 
which  is  fastened  to  the  bed  of  the  press  and  the  lower 
piston  is  operated  by  means  of  the  Throw-out  Rod  "L" 
connected  to  the  lower  plunger  of  the  press. 

The  operation  is  as  follows: 

The  mold  is  filled  with  the  material  to  be  pressed 
as  in  the  case  of  Figure  3,  and  the  piece  is  compressed 


118 


MOLDED    INSULATION 


in  a  similar  manner.  At  this  point  the  similarity  ceases. 
After  the  piece  is  pressed,  the  Upper  Piston  "C"  is  with- 
drawn from  the  mold  and  the  Lower  Piston  "B"  is  raised 
by  the  Throw-out  Rod  "L,"  and  by  this  means  the  piece 
is  expelled  from  the  mold.  The  Piston  "B"  now  descends 
to  its  normal  position  at  the  bottom  of  the  mold  and 
it  is  then  ready  for  re-filling  without  having  to  undergo 
any  heating  or  cooling  operations. 

When  dies  of  this  type  are  employed,  the  materials 
are  either  weighed  or  measured  beforehand,  and  just  suffi- 
cient is  introduced  into  the  die  to  form  the  piece. 


B 


FIG.  6 


Figure  6  shows  a  molded  piece  with  a  metallic  insert 
"A"  molded  in.     Such  pieces  can  be  easily  produced  in 


MOLDS   AND    DIES 


119 


materials  of  Classess  "A,"  "B,"  "C,"  "E,"  "F"  and 
"G."  However,  if  absolute  accuracy,  together  with  a 
highly  polished  piece  is  required  only  Classes  "A,"  "E," 
"F"  and  "G"  can  be  considered.  Class  "B"  could  be 
advantageously  molded  into  this  shape,  but  a  slight  varia- 
tion must  be  tolerated  and  only  the  exterior  surface  can  be 
polished.  Class  "C"  could  be  molded  accurately,  but  it 
would  be  necessary  to  increase  the  radius  at  "B"  as 
much  as  possible. 


FIG.  7 


Figure  7  shows  the  design  of  the  mold  from  which 
this  piece  is  produced,  and  is  here  represented  to  illus- 
trate the  manner  in  which  inserts  are  molded  into  the 
materials.  These  inserts  should  be  provided  either  with 


120  MOLDED   INSULATION 

a  knurled  or  some  other  rough  and  irregular  surface 
so  that  they  may  be  firmly  gripped  by  the  material. 

Another  point  of  interest  is  the  production  of  letters 
or  figures  on  molded  pieces. 

On  materials  such  as  those  of  Classes  "A,"  "E,"  "F" 
and  "G,"  where  the  pieces  come  from  the  molds  in  a 
polished  condition,  no  difficulty  is  experienced  in  produc- 
ing raised  letters.  However,  if  such  materials  as  those  of 
Classes  "B"  and  "C"  are  used,  where  the  pressed  pieces 
do  not  come  from  the  molds  in  a  finished  condition,  but 
must  be  hardened,  ground,  and  polished,  raised  lettering 
cannot  be  used,  as  the  grinding  and  polishing  of  the 
surface  would  destroy  them.  Therefore,  it  is  essential 
in  all  cases  where  pieces  are  to  be  made  of  materials 
in  Classes  "B"  and  "C,"  that  the  designer  employ  some 
other  means  to  incorporate  the  lettering  on  his  pieces. 
An  excellent  method  and  one  which  has  become  a 
standard  for  use  in  connection  with  these  materials  is 
to  recess  a  portion  of  the  surface,  leaving  the  letters 
raised  and  flush  with  the  main  surface,  so  that  the 
tops  of  letters  receive  the  same  polish  as  the  rest  of 
the  surface. 

Metal  inserts  are  never  molded  in  pieces  made  of 
the  ceramic  materials.  Openings  or  recesses  are  molded, 
into  which  the  metal  parts  are  inserted  and  held  in 
place  by  riveting  or  other  mechanical  means.  Usually 
sealing  wax  or  some  other  form  of  cement  is  used  to 
fill  the  recesses,  covering  the  screw  heads  or  nuts  to  pre- 
vent the  exposure  of  live  parts. 

Figure  8  shows  a  typical  cross  section  of  a  molded 
insulating  box  or  cover,  and  illustrates  very  nicely  some 
of  those  elements  of  design  constituting  a  part  of  that 
unwelcome  legacy  which  comes  to  the  molded  insulation 
manufacturer  from  his  predecessors  who  worked  with 


MOLDS   AND    DIES 


121 


.  A 


•  • 


R^S^WsN^^ 
^ 


\ 


B 


FIG.   8 


FIG.   9 


materials  of  a  very  different  nature. 

This  cross  section  shows  a  cover  or  box  having 
thin  walls  and  sharp  interior  corners.  In  other  words,  a 
typical  metal  box  or  cover,  which  offers  no  difficulty 
whatever  to  the  metal  stamper,  but  which  is  not  well 
adapted  to  meet  the  requirements  of  the  modern  molded 
insulating  materials;  it  is  a  good,  if  very  simple,  ex- 
ample of  the  trouble  designers  often  make  for  them- 
selves and  the  molded  insulation  manufacturer  by  failing 
to  bear  in  mind  that  the  characteristics  of  modern  ma- 
terials differ  from  those  formerly  in  common  use.  If, 
as  often  happens,  the  apparatus,  of  which  this  cover 
is  to  form  a  part  has  been  made,  or  the  component  metal 
parts  which  compose  it  are  already  under  construction 
or  ordered  from  some  other  sources  before  the  molded 
insulation  manufacturer  is  consulted,  the  designer  of  such 
a  cover  may  find  himself  in  trouble  and  be  fortunate 


122 


MOLDED    INSULATION 


if  he  has  put  himself  to  no  greater  inconvenience  than  to 
greatly  restrict  the  number  of  materials  from  which  this 
part  can  be  made. 

The  design  of  this  cover,  Figure  8,  is  entirely  un- 
suited  for  manufacture  from  materials  of  Classes  "B," 
"C"  and  "D,"  which  are  among  the  best  materials 
from  which  to  make  such  parts  as  switch  and  fuse  box 
covers,  owing  to  their  high  heat-resisting  qualities,  but 
the  straight  thin  sides  of  the  box  practically  make  it 
impossible  to  form  this  piece  of  these  materials,  and  it 
would  be  very  difficult  to  properly  mold  the  thin  parallel 
sides,  as  the  material  would  not  be  compactly  pressed 
at  the  top  of  the  sides,  Point  "A,"  unless  a  complicated 
mold  were  employed,  which  would  exert  the  necessary 
extra  pressure. 


FIG.  10 


FIG.  11 


Should  there  be  room  inside  the  box  to  thicken  the 
side     walls     particularly     at     their     base     point     "B" 


MOLDS   AND    DIES  123 

Figure  9,  and  so  give  the  sides  a  taper  or  draw,  the  design 
would  be  improved.  Even  this  added  thickness  is  not 
sufficient  in  most  cases,  as  it  would  be  of  great  advantage 
to  put  as  large  a  radius  as  possible  in  the  corners  "C," 
as  is  shown  in  Figure  10. 

Figure  11  shows  a  cover  having  the  proper  thickness 
of  walls,  with  the  necessary  draw  or  taper  to  the  inside, 
and  a  generous  fillet  or  curve  in  the  corners  to  make 
it  an  ideal  design  for  the  proper  flowing  and  molding  of 
the  materials  of  Classes  "B,"  "C"  and  "D."  This  form 
is  equally  well  suited  to  materials  of  Classes  "A,"  "E," 
"F"  and  "G,"  although  the  free  flowing  qualities  of 
these  materials  do  not  make  it  imperative  that  the  piece 
be  designed  in  this  manner. 

Figure  12  shows  a  receptacle  box  of  rather  intricate 
form.  Formerly  such  pieces  were  made  exclusively  in 
porcelain,  but  are  now  also  extensively  manufactured  in 
the  cold  molded  materials  of  Classes  "B"  and  "C." 

The  synthetic  resinous  materials  of  Class  "G"  are 
splendidly  adapted  to  producing  pieces  of  this  character, 
but  they  are  very  rarely  used  because  of  their  high 
cost  in  comparison  with  Classes  "B,"  "C"  and  "D." 

In  a  previous  illustration,  particular  stress  has  been 
laid  on  the  desirability  of  designing  such  pieces  with 
thick  walls  and  ample  radius  at  the  bottom,  particularly 
when  made  of  materials  in  Classes  "B"  and  "C."  Too 
much  emphasis  cannot  be  laid  on  these  points. 

Figure  12  shows  that  it  is  possible  to  produce  pieces 
of  this  design  in  these  materials,  but  it  is  not  accom- 
plished without  some  difficulty,  and  in  some  cases  it 
requires  a  very  complicated  mold.  It  also  becomes  nec- 
essary to  sacrifice  the  mechanical  strength  in  order  to 
have  a  mixture  of  material  which  has  the  viscosity 
necessary  to  meet  the  molding  requirements. 


124 


MOLDED    INSULATION 


x- 


SECTION  x-r 

FIG.    12 


A  much  more  satisfactory  design  for  both  the  cus- 
tomer and  manufacturer  would  have  resulted  if  walls 
"A,"  "B,"  "C"  and  "D"  were  made  somewhat  thicker; 


MOLDS   AND    DIES  125 

also  by  the  addition  of  a  radius  at  Points  "E,"  "F" 
and  "G." 

In  molding  pieces  of  this  character  in  porcelain,  it 
has  been  the  custom  to  allow  for  a  variation  in  the  dis- 
tance "H"  by  making  the  holes  about  1/32"  larger  than 
the  diameter  of  the  screws  which  fit  in  these  holes. 

Although  the  manufacturers  of  materials  of  Class 
"B"  generally  claim  that  they  can  mold  such  pieces 
more  accurately  than  those  made  in  porcelain,  it  would 
be  advisable  for  the  designer  not  to  figure  on  absolute 
accuracy  in  a  piece  of  this  nature,  if  he  intends  to  have 
them  made  of  this  material.  He  should  allow  for  a 
few  thousandths  of  an  inch  variation. 

Designers  frequently  assert  that  they  are  limited 
as  to  space,  both  inside  and  outside,  of  such  parts,  but, 
with  a  better  understanding  of  the  fundamental  require- 
ments of  the  molding  art,  and  a  fuller  realization  of  the 
difficulties  they  make  for  the  insulation  manufacturer,  and 
the  consequent  higher  cost  and  poorer  quality  of  the  pieces 
they  obtain,  they  can  originate  pieces  better  adapted  to 
molding  in  the  materials  they  require. 

By  giving  a  little  more  consideration  to  the  molded 
insulating  parts  before  the  design  of  the  apparatus,  in 
which  those  parts  are  to  be  incorporated,  has  become  ir- 
revocably fixed,  designers  would  materially  help  them- 
selves as  well  as  the  insulating  manufacturer. 

Figures  13  and  14  show  two  insulated  knurls  of 
different  design,  serving  the  same  purpose,  and  the  molds 
for  producing  them. 

Figure  13  shows  the  original  or  incorrect  design 
and  Figure  14  the  same  piece  altered  to  facilitate  the 
molding,  increase  the  production,  improve  the  appear- 
ance of  the  piece,  and  to  make  the  mold  much  easier 
and  N  less  complicated  to  manufacture  and  handle. 


126 


MOLDED    INSULATION 


FIG,    13 


The  piece  shown  in  Figure  13  presents  numerous 
difficulties.  The  groove  "A"  on  the  side  and  also-  this 
type  of  knurling  makes  it  absolutely  necessary  for  the 
piece  to  be  surrounded  by  a  number  of  loose  parts 
which  must  be  removed  from  the  Box  "C"  in  order 


MOLDS    AND    DIES  127 

to  free  the  piece  from  the  same.  This  can  readily  be 
seen  from  the  section  shown.  At  the  junction  of  these 
loose  parts,  a  finn  or  burr  will  be  formed  which  must 
be  removed,  thus  increasing  the  cost  of  manufacture 
and  affecting  the  appearance  of  the  piece. 

Another  bad  feature  of  this  design  is  the  thread 
molded  in  the  material  above  the  metal  insert  "B." 
As  all  molded  insulating  materials  shrink  more  or  less, 
the  threads  in  the  molded  material  will  be  smaller  than 
those  in  the  insert. 

On  the  other- hand,  the  design  as  shown  in  Figure  14 
is  much  simpler  and  less  complicated.  The  groove  on 
the  side  is  entirely  eliminated  and  the  style  of  knurling 
is  changed  from  braided  to  straight,  thus  making  it  pos- 
sible to  push  the  piece  from  the  mold  by  merely  press- 
ing it  from  the  bottom  towards  the  top.  This,  of  course, 
does  away  with  the  loose  parts  and  eliminates  all  burrs 
and  produces  a  perfectly  clean,  smooth,  and  neat  appear- 
ing piece. 

It  will  also  be  noticed  in  this  figure  that  the  insert 
"B"  has  been  lengthened  to  accommodate  the  full  depth 
of  thread  which  would  otherwise  be  partly  molded  in  the 
material.  The  sloping  sides  or  pointed  appearance  on  the 
end  is  to  allow  the  material  to  flow  off  and  around  it 
instead  of  packing  tightly  and  crushing  on  the  top  as 
it  would  do  if  it  were  flat. 

Therefore,  the  design  as  shown  in  Figure  14  is 
strongly  recommended  whenever  it  is  possible  for  two 
important  reasons : 

First:     The  lower  cost  of  production. 

Second :  The  freedom  from  burrs  which  will  form 
at  the  junction  of  the  split  portions  of  the  mold  made 
necessary  by  the  groove  on  the  side,  and  the  use  of  this 
type  of  knurling. 


128 


MOLDED    INSULATION 


These  conditions  apply  not  only  to  insulated  knurls, 
but  to  any  pieces  of  similar  design  or  construction. 


c 

D 

©b 

(o) 

o 

© 

(sy 

©@ 

FIG.    15 

Figure  15  represents  a  molded  base  with  a  projec- 
tion "A"  and  numerous  counterbored  holes.  A  piece 
of  this  design  is  readily  molded  of  the  hot  molded  ma- 
terials "A,"  "E,"  "F"  and  "G,"  also  of  the  ceramic 
materials,  Class  "D."  It  can  also  be  molded  of  ma- 
terials of  Classes  "B"  and  "C,"  if  certain  changes  in 
design  are  made. 

In  the  first  place  the  flowing  qualities  of  these  ma- 
terials, Classes  "B"  and  "C,"  make  it  difficult  to  mold 
such  shapes  as  projection  "A,"  unless  molds  of  com- 


MOLDS   AND    DIES 


129 


plicated  construction  are  resorted  to.  Such  pieces  can 
be  made  perfectly  practical  for  cold  molding  by  the 
introduction  of  two  simple  modifications. 

First  by  the  addition  of  a  radius  around  the  base, 
as  is  shown  at  "  B "  in  Figure  16,  and  secondly  by  giving 
a  slight  draw  or  taper  to  the  sides,  which  is  also  shown 
in  this  same  figure. 


Co." 
C°." 

0) 
P) 

loj 

O  i'5  '] 

\J  (0) 

I     I 


I     I 


FIG.    16 

With  these  modifications,  such  a  projection  can  be 
readily  molded  true  in  form,  neat  in  appearance,  and 
with  the  proper  mechanical  strength. 

It  is  possible  to  mold  pieces  with  this  projection 
exactly  as  is  shown  in  Figure  15,  but  the  modifications 
suggested  are  simply  to  increase  production  and  to  reduce 
the  cost. 


130  MOLDED    INSULATION 

Another  point  is  the  shape  of  the  counterbores.  In 
Figure  15,  two  counterbores  are  shown  which  are  so 
close  together  as  to  leave  a  very  thin  separating  wall, 
as  at  point  "C."  At  point  "D"  there  is  also  a  very 
thin  wall  produced  between  a  single  counterbore  and  the 
side  of  the  piece.  When  wood  and  fibre  were  extensively 
used  and  insulating  pieces  were  machined  from  blocks 
and  sheets,  this  was  a  logical  design,  but  it  is  not  now 
well  suited  to  the  peculiarities  of  modern  insulating 
mediums. 

In  order  to  adapt  this  piece  to  the  present  require- 
ments of  cold  molded  materials,  it  would  be  advisable 
to  eliminate  these  thin  walls  by  cutting  them  away, 
as  is  shown  in  Figure  16,  thus  making  one  elongated 
counterbore,  and  opening  the  other  to  the  outside  of 
the  piece. 

If,  howrever,  it  be  necessary  to  have  a  barrier  of 
this  kind  separating  these  counterbores  owing  to  elec- 
trical requirements,  the  designer  should  place  these  holes 
far  enough  apart  and  away  from  the  edge  of  the  insulat- 
ing piece  so  as  to  allow  a  wall  of  ample  thickness. 

In  all  cases,  the  depth  of  the  counterbores  should  be 
no  greater  than  the  requirements  of  the  piece,  and  ample 
draw  or  taper  should  be  allowed  on  the  sides  of  the  same 
in  order  to  allow  the  easy  removal  of  the  piece  from  the 
surface  of  the  pistons  in  the  mold. 

All  holes  should  be  made  as  large  as  convenient 
for  their  purpose,  so  that  the  pins  in  the  mold  which 
form  them  may  be  as  rugged  as  possible. 

Figure  17  is  a  typical  piece  of  molded  insulation 
used  as  a  strain  insulator  in  overhead  line  construction 
and  shows  how  the  insulating  material  is  molded  around 
the  metal  parts. 

The   hot    molded    materials    of   Classes    "A,"    "E" 


MOLDS   AND    DIES 


131 


FIG.    17 

and  "G"  are  well  suited  to  the  manufacture  of  such 
parts,  and  while  formerly  the  rubber  compounds  of  Class 
"E"  were  extensively  used,  to-day  the  materials  of  Class 
"A"  practically  monopolize  this  field,  chiefly  on  account 
of  their  lower  cost. 

For  this  latter  reason  the  synthetic  resinous  products 
of  Class  "GM  have  not  come  in  use  for  such  purposes, 


132          ..      MOLDED   INSULATION 

their  cost  being-  too  high,  although  the  properties  of 
this  material  seem  to  indicate  that  it  would  stand  up 
well  as  an  insulator  under  the  severe  climatic  conditions 
to  which  such  insulators  are  exposed. 

The  cold  molded  materials  of  Classes  "B"  and  "C" 
are  used  for  the  manufacture  of  such  pieces,  but  to  a 
limited  extent.  As  they  do  not  possess  the  necessary, 
plasticity  to  be  molded  as  easily  as  the  hot  molded  pro- 
ducts, the  molding  of  such  parts  causes  difficulties  owing 
to  the  high  pressure  required  to  obtain  perfect  molded 
pieces. 

The  hot  molded  materials  of  Classes  "A,"  "E"  and 
"G"  are  readily  molded  with  comparatively  little 
pressure  while  in  a  hot  plastic  condition  around  the  two 
metal  parts  which  are  held  in  position  at  the  outer  ends 
by  the  die. 

In  ease  of  molding  materials  of  less  plastic  nature, 
such  as  Classes  "B"  and  "C."  around  these  two  metal 
parts,  such  materials  do  not  flow  easily  around  the  metal 
inserts,  but  have  to  be  forced  around  them  by  means 
of  high  pressure.  These  inserts,  held  in  position  only 
by  the  die  at  their  extremities  "A"  and  "B," 
and  having  no  central  support,  are  apt  to  be  distorted, 
rendering  the  finished  piece  imperfect  and  useless  for 
service. 

The  Figure  18  illustrates  a  magneto  insulator 
as  is  commonly  used  for  automobile  work.  Formerly 
such  parts  were  made  either  of  materials  of  the  rubber 
compounds  of  Class  "E"  or  else  of  special  .grade  ma- 
terials of  the  organic  hot  molded  products  of  Class  "A." 

As  the  magnetos  are  usually  placed  near  the  hot 
engines,  and  the  insulating  parts  come  in  contact  with 
hot  oils  and  gasoline  vapors,  considerable  trouble  was 
previously  experienced  with  the  materials  above  men- 


MOLDS   AND    DIES 


133 


FIG.    18 


tioned  for  parts  of  this  nature.  This  trouble  was 
caused  by  either  the  materials  not  being  heatproof 
enough  or  else  by  being  affected  by  the  oil  and  gasoline 
vapors. 


134  MOLDED    INSULATION 

The  ceramic  materials  of  Class  "D"  could  not  be 
used,  as  the  molding  could  not  have  been  done  accurately 
enough  or  no  metal  parts  could  have  been  molded  in,  and 
also  these  materials  could  not  stand  the  vibration  to 
which  they  would  necessarily  be  subjected  in  an  auto- 
mobile. 

The  inorganic  cold  molded  materials  of  Class  "C" 
could  not  have  been  satisfactorily  employed  for  the 
molding  of  these  parts  for  two  reasons.  They  could  not 
be  molded  accurately  enough,  and  furthermore,  as  such 
parts  should  be  safe  to  withstand  at  least  3,000  volts 
continuously,  the  insulating  properties  of  this  product 
would  not  be  sufficient. 

The  materials  of  Class  "B"  could  not  be  molded 
accurately  enough,  and  they  are  primarily  adaptable  for 
use  under  working  conditions  below  1,000  volts. 

The  products  best  suited  for  such  parts  and  which 
fulfill  all  the  requirements  are  the  materials  of  Class 
"G."  These  materials  are  already  almost  entirely  em- 
ployed for  such  purposes. 

In  the  molding  of  such  shapes  of  materials  of  Classes 
"B"  and  "C,"  the  four  inserts  A,  B,  C  and  D  would 
present  some  difficulties  owing  to  the  high  pressure  re- 
quired in  the  pressing.  These  inserts,  as  shown  in  Figure 
18,  can  only  be  supported  at  their  extremities,  and  there 
would  be  great  danger  of  their  distorting  between  the 
supporting  points. 

Therefore,  the  principal  feature  to  bear  in  mind 
is  the  position  and  shape  of  the  inserts,  and  that  they 
be  designed  and  located  so  that  they  may  be  easily  and 
firmly  held  in  'position  and  sufficiently  supported  so 
that  they  will  not  bend  or  distort  during  the  molding 
process. 


SELECTION   OF   MATERIALS  135 


SELECTION  OF  MATERIALS  IN  RELATION  TO 
DESIGN  AND  USES  OF  INSULATING  PARTS 


The  molding,  physical,  mechanical,  electrical,  and 
other  properties  of  the  different  classes  of  materials. 
as  they  affect  their  relative  adaptability  to  the  produc- 
tion of  various  molded  articles,  has  been  treated  in 
previous  chapters.  This  question  is,  however,  of  such 
vital  importance  to  the  designer  and  electrical  engineer 
that  the  author  has  thought  it  advisable  to  offer  some 
further  suggestions,  aided  by  illustrations,  which,  it  is 
hoped,  will  prove  helpful  to  those  having  to  select  the 
material  best  suited  to  their  purpose  from  among  the 
classes  treated  in  this  work.  Since  entirely  legitimate 
differences  of  opinion  must  exist  as  to  what  may  be  re- 
quired of  an  insulating  material  for  a  given  purpose, 
these  suggestions  are  evidently  not  offered  as  final  or  as 
applying  to  every  circumstance  that  may  arise. 

The  author's  long  and  intimate  experience  in  manu- 
facturing materials  of  all  of  the  classes  treated,  as  well 
as  his  personal  and  business  relations  with  the  foremost 
electrical  designers  and  engineers,  permitting  him,  as 
they  do,  to  base  these  suggestions  on  the  experience  of 
the  past  ten  years  both  in  the  laboratory  and  in  actual 
service,  leads  him  to  believe  that  they  will  be  of  some 
assistance  to  those  seeking  information.  No  reference  to 
Class  "H,"  the  fibre  products,  will  be  made,  for,  as 
previously  stated,  materials  of  this  class  are  principally 


136  MOLDED    INSULATION 

used  in  the  form  of  sheets,  rods,  and  tubes  only,  and 
machined  into  the  desired  shapes.  Class  "I,"  mica 
molded  articles  is  also  excluded,  they  being  restricted 
to  the  usual  known  micanite  segments,  rings,  tubes, 
sheets  and  such  forms.  When  referring,  therefore,  to 
parts  which  may  be  molded  of  materials  of  all  classes, 
it  must  be  understood  that  Classes  "H"  and  "I"  are 
not  included. 


PLATE 


PLATE  II 


ILLUSTRATIONS  139 


Plates  Nos.  I.  and  II. 

Parts  of  familiar  design  are  here  shown,  which  may  be 
molded  from  materials  of  all  of  the  six  classes,  though  for  prac- 
tical reasons,  the  ceramic  products  of  Class  "D"  are  almost  ex- 
clusively used  at  the  present  time  in  the  production  of  these 
and  similar  parts.  This  is  partly  due  to  the  excellent  dielectric 
and  physical  characteristics  of  porcelain,  but  principally  to  its 
low  cost.  As  a  result,  the  combined  production  of  such  parts 
from  materials  of  the  other  classes  is  far  below  that  of  Class 
"D,"  the  ceramic  products. 

Ten  years  ago,  porcelain  alone  was  available  for  such  parts, 
but  since  that  time  other  'classes  of  molded  materials,  such  as 
those  of  Classes  "B"  and  "C"  have  grown  in  favor,  so  that 
at  the  present  time  the  designer  of  electrical  appliances  is  no 
longer  limited  to  porcelain,  but  has  at  his  disposal  both  the 
inorganic  and  organic  cold  molded  materials  of  Classes  ""B" 
and  "C,"  giving  him  a  wider  range  as  to  appearance  and 
physical  qualities,  where  very  low  cost  is  not  an  absolute  essential. 

The  hot  molded  materials  of  Class  "A"  are  also  available, 
and  sometimes  used  where  resistance  to  heat  is  not  required. 
Also  the  synthetic  resinous  materials  of  Class  "G,"  but  only 
when  cost  need  not  be  considered. 


PLATE  III 


ILLUSTRATIONS  141 


Plate  No.  III. 

VARIOUS  TYPES  OP  SWITCH  HANDLES 

Appearance  and  finish  are  the  essentials  in  such  parts.  They 
are  also  generally  molded  with  metal  studs  or  blades  in  place. 
The  production  of  such  .parts  is  practically  limited  to  the  hot 
molded  materials  of  Class  "A,"  which,  high  heat-resistance 
not  being  of  importance,  best  fill  the  requirements  as  to  finished 
appearance  and  low  cost.  The  synthetic  resinous  materials  of 
Class  "G-"'  are  also  entirely  suitable,  but  are  debarred  owing  to 
their  high  cost. 

The  cold  molded  materials  of  Classes  "B"  and  "C"  may 
be  molded  into  such  shapes,  but  owing  to  the  uneven  surfaces, 
they  cannot  be  polished  and  finished  as  well  as  materials  of 
Class  "A." 

The  ceramic  products  of  Class  '  *  I) ' '  were  at  one  time  em- 
ployed to  a  limited  extent,  but  have  now  been  almost  entirely 
superseded. 

Materials  of  Class  <'E"  (rubber  compounds)  are  no  longer 
used  for  such  purposes. 


PLATE   IV 


ILLUSTRATIONS  143 


Plate  No.  IV. 

A  FURTHER  VARIETY  OF  SMALL  SWITCH  HANDLES  AND 

KNOBS   OFFERING   MORE   LATITUDE    IN   THE    CHOICE 

OF    MATERIALS    THAN    THOSE    SHOWN    IN    PLATE 

NO.  Ill 


The  first  points  for  consideration  in  selecting  a  material 
for  these  parts  being  cost  and  appearance,  the  products  of 
Class  "A"  are  most  adaptable,  though  these  forms,  being  more 
regular  than  those  shown  in  Plate  No.  Ill,  and  being  readily 
and  rapidly  polished,  may  also  be  produced  of  the  products  of 
Class  "B,"  with  very  little  increase  in  the  cost.  In  cases  where 
heat-resistance  is  required,  the  materials  of  Class  "B"  are,  there- 
fore, used,  being  very  little  inferior  to  those  of  Class  "A"  in 
appearance,  and  possessing  all  of  the  other  desirable  properties. 

The  ceramic  products,  Class  "D"  are  not  used  for  such 
parts,  and  materials  of  Class  "G, "  synthetic  resinous  products, 
while  entirely  suitable,  can  only  be  used  when  cost  need  not 
be  considered. 

The  inorganic  materials  of  Class  "C"  are  not  used,  owing 
to  their  inferior  finish,  while  the  rubber  compounds  of  Class  "E, " 
at  one  time  employed,  are  now  rarely,  if  ever,  seen. 


PLATE  V 


ILLUSTRATIONS  145 


Plate  No.  V. 

MOLDED   ARTICLES   MOSTLY   FOUND    IN    TELEPHONE 

WORK 


Eesistance  to  heat  being  unimportant,  materials  of  Classes 
"A"  and  "E"  are  most  suitable,  particularly  for  parts  illus- 
trated by  Figures  A  and  B,  owing  to  the  high  and  permanent 
finish  required,  and  by  Figure  C,  owing  to  the  multiplicity  of 
small  and  delicate  metal  parts  which  are  molded  into  the 
material. 

While  materials  of  Class  lt  G ; '  are  in  every  way  suitable,  their 
comparatively  high  cost  has,  up  to  now,  precluded  their  general 
use. 

The  materials  of  Classes  "B"  and  "C"  are  entirely  unsuit- 
able for  the  style  of  pieces  shown  by  Figures  A  and  B,  though 
in  some  cases  they  might  prove  satisfactory  for  pieces  similar 
to  Figure  C. 

Materials  of  Classes  "B"  and  "C"  are  suitable  for  molding 
parts  shown  in  Figures  D,  E  and  F,  particularly  the  latter  in 
the  larger  sizes,  or  where  used  in  installations  in  which  they 
may  be  exposed  to  heat. 


PLATE  VI 


ILLUSTRATIONS  147 


Plate  No.  VI. 

OVERHEAD  LINE  INSULATORS 


Formerly,  these  parts  were  made  of  the  rubber  compounds  of 
Class  "E,"  but  today  they  are  almost  exclusively  made  of  the 
organic  hot  molded  materials  of  Class  "A." 

Materials  of  Classes  "B"  and  "C, "  while  desirable  owing 
to  their  heat-resisting  qualities  in  case  of  line  short  circuits, 
have  not  been  successfully  used,  due  to  difficulties  in  molding 
the  forms  and  metal  inserts  required,  as  has  been  more  fully  ex- 
plained in  considering  similar  parts  in  a  previous  chapter. 

Materials  of  Class  "G"  would  be  ideal  for  this  purpose 
were  it  not  for  their  high  cost.  Whether  or  not  this  may  be 
justified  by  their  superior  properties  has  not  yet  been  definitely 
determined,  as  the  synthetic  resinous  products  are  of  too  recent 
origin  and  sufficient  comparative  data  as  to  behavior  under  service 
conditions  is  not  available. 


PLATE  VII 


ILLUSTRATIONS  149 


Plate  No.  VII. 

MAGNETO    DISTRIBUTOR,    COLLECTOR,    AND    SIMILAR 
•     PARTS 


Hot  molded  materials  are  only  suitable  for  molding  such 
parts,  as  has  been  more  fully  explained  in  considering  a  similar 
piece  in  the  chapter  on  molds  and  dies. 

In  the  past,  materials  of  Classes  "A"  and  "E"  were  used, 
but  recently  they  have  been  superseded  by  the  synthetic  resinous 
materials  of  Class  "G';  which  are  pre-eminently  adopted  for  this 
purpose  to  the  exclusion  of  materials  of  any  of  the  other  classes. 
Owing  to  their  heat-resisting  qualities  and  lower  cost,  repeated 
efforts  have  been  made  to  render  the  materials  of  Classes  "B" 
and  "C"  adaptable  to  this  purpose,  but  as  yet  without  any 
marked  success. 


ID 

x-*::— — *       Jf ~~~tj~  ~~"_.r~^ Iz  -^ 


PLATE  VIII 


ILLUSTRATIONS  151 


Plate  No.  VIII. 

A    FURTHER    SERIES    OF    PARTS    SIMILAR    TO    THOSE    OF 
PLATE  NO.  VII 


These  parts  are  best  made  of  the  hot  molded  materials  of 
Classes  "A"  and  "G."  Formerly,  only  the  materials  of  Class 
"A"  were  available,  but  to-day  the  synthetic  resinous  materials  of 
Class  "G"  receive  favorable  consideration  where  cost  is  of 
secondary  importance. 

Cold  molded  materials  of  Classes  "B"  and  "C"  are  not 
recommended,  and  the  ceramics  of  Class  "D77  are  entirely  unsuit- 
able. Pieces  of  this  style,  shown  by  Figures  A  and  B  particularly, 
can  only  be  successfully  produced  in  materials  of  Classes  "A" 
and  "G." 

In  Figure  A,  this  is  due  to  the  insulated  wires  which  could 
not  be  properly  molded  into  place  under  the  cold  molding  pro- 
cesses, and  would  further  be  rendered  useless  through  the  destruc- 
tion of  their  insulating  cover  by  the  high  temperatures  to  which 
these  products  are  usually  subjected  after  the  pressing  operation. 

In  Figure  B,  this  is  due  to  the  metal  parts  which  could  not 
be  successfully  molded  in  under  the  cold  molding  processes. 

In  fact,  the  accuracy  of  dimensions  and  complication  of 
shapes  required  in  parts  shown  in  this  cut  can  only  be  produced 
with  facility,  in  the  materials  of  Classes  "A"  and  "G,"  and 
therefore,  materials  of  Classes  "B"  or  "C77  should  only  be  con- 
sidered in  special  cases  where  the  peculiar  characteristics  of 
these  materials  may  be  necessary. 


\ 


\ 


PLATE   IX 


ILLUSTRATIONS  153 


Plate  No.  IX. 

A   SERIES    OF    INSULATING   HANDLES 


In  the  United  States,  these  parts  have  up  to  the  present 
time  been  almost  entirely  made  of  wood,  though  to  a  lesser 
-extent,  materials  of  Class  "A'  have  been  used,  and  very  re- 
cently materials  of  Classes  "B"  and  "C"  have  been  con- 
sidered. 

,  It  would  seem  strange  that,  while  in  Europe,  more  especially 
in  Germany,  the  strict  regulations  of  Fire  Underwriters  have 
-debarred  wood  as  unsafe,  no  strong  movement  has  taken  place 
in  the  United  States  in  favor  of  molded  materials,  though  this 
is  probably  due  to  the  cheapness  of  wood. 

It  is,  however,  the  author's  belief  that,  as  fibre  and  wood 
have  been  superseded  by  molded  materials  for  other  purposes,  they 
will,  in  the  near  future,  be  displaced  by  molded  materials. 

The  higher  cost  will  be  more  than  compensated  by  superior 
-dielectrical  and  physical  qualities.  Such  switch  handles  are  used 
under  varying  conditions  of  heat  and  moisture,  rendering  them 
liable,  when  made  of  wood,  to  shrink  or  expand,  with  the  result 
that  metal  parts  will  split  the  handles  or  become  loose,  and  in 
consequence  be  a  source  of  actual  danger. 

Owing  to  the  great  number  of  suitable  molded  materials 
available,  no  difficulty  should  be  experienced  in  selecting  a 
satisfactory  product.  For  this  purpose  the  synthetic  resinous 
materials  of  Class  "G"  are  the  best  where  cost  need  not  be  con- 
sidered, but  are  closely  followed  by  the  hot  molded  materials 
of  Class  f<A"  and,  more  recently,  by  the  cold  molded  materials 
of  Class  "B." 


D 


I    Of 


PLATE  X 


ILLUSTRATIONS  155 


Plate  No.  X. 

A    SERIES    OF    CHARGING    OR    CONTACT    PLUGS    AND 
SIMILAR  PARTS 


These  pieces  being  subjected  to  very  rough  treatment  in 
service,  require  a  material  which  is  tough  and  will  not  chip  or 
crack  under  hard  blows. 

Owing  to  the  high  amperages  generally  carried  by  these  parts, 
heat-resistance  is  an  essential  to  prevent  any  danger  of  fire  or 
deterioration  of  the  insulation  by  charring,  when  contacts  are 
made  and  broken.  Until  recently  materials  of  Class  "A"  were 
used,  but  they  have  now  been  discarded  as  unsafe  owing  to 
their  lack  of  resistance  to  heat.  Vulcanized  fibre  is  at  present 
very  much  in  favor  owing  to  its  toughness  and  non-inflammability, 
but  still  leaves  much  to  be  desired  as  it  will  in  time  char,  and 
is  very  sensitive  to  conditions  of  moisture  and  dryness  in  -the 
atmosphere  which  cause  it  to  distort  with  a  consequent  displace- 
ment of  metal  contact  parts.  In  view  of  the  .above,  and  the 
further  fact  that  fibre  must  be  machined  to  obtain  the  desired 
shapes,  it  would  seem  that  the  molded  products  will  in  the 
very  near  future  be  called  on  to  advantage  and  fibre  entirely 
superseded. 

Materials  of  Classes  "B,"  "G"  and  "G"  will  be  found 
well  adapted  to  this  purpose,  owing  to  their  high  heat-resistance 
and  indifference  to  moisture,  "B"  and  "G"  being  used  where 
cost  is  a  consideration,  and  "G"  for  parts  of  intricate  shapes 
where  cost  may  be  disregarded. 

The  ceramics,  Class  "D,"  are  entirely  unsuitable,  and  the 
rubber  compounds  of  Class  "E"  are  seldom  used. 

The  parts  shown  in  the  plate  with  the  exception  of  Figure  A, 
made  of  synthetic  resinous  material,  Class  "G,"  and  Figure  B, 
made  of  hot  molded  organic  material  of  Class  "A,"  are  all 
made  of  the  cold  molded  materials  of  Classes  "B"  and  "G" 
and  have  been  in  successful  commercial  use  for  a  number  of 
years. 


«•  «: 

* 


•  • 


!•  Aft 


PLATE   XI 


ILLUSTRATIONS  157 


Plate  No.  XI. 

VARIOUS     CONNECTOR     OR     PLUG     PARTS     PRINCIPALLY 

USED    WITH    ELECTRIC    FLAT    IRONS    AND    OTHER 

ELECTRICAL    HEATING    APPLIANCES 


The  primary  requisite  for  such  parts  is  resistance  •  to  heat, 
as  they  must  necessarily  come  in  direct  contact  with  the  hot 
metal  parts  of  the  appliances  which  they  connect  to  the  source 
of  current.  Under  normal  conditions,  300°  C.  without  softening 
or  other  deterioration  is  the  usual  temperature  limitation. 

Furthermore,  these  parts  being  furnished  as  part  of  a 
household  article,  must  be  well  finished  in  appearance. 

Before  the  introduction  of  the  cold  molded  organic  ma- 
terials of  Class  "B,"  the  only  available  products  were  porcelain, 
and  some  molded  material  depending  on  a  large  proportion 
of  asbestos  for  the  necessary  heat-resistance. 

The  former,  owing  to  its  brittleness  and  consequent  liability 
to  chipping  has  been  almost  totally  abandoned,  except  in  a  few 
cases,  where  it  is  protected  by  an  outer  metal  casing.  The 
latter,  owing  to  its  heavy  asbestos  content,  was  rough  and  un- 
sightly, and,  therefore,  discarded. 

At  the  present  time,  materials  of  Class  "B"  above 
referred  to,  are  almost  exclusively  used,  though  in  some  exceptional 
cases  of  special  design,  materials  of  Class  "G"  are  preferred, 
owing  to  their  higher  heat-resistance.  Materials  of  Classes  ' '  E ; ' 
and  "G"  are  not  used,  partly  owing  to  their  prohibitive  cost, 
but  principally  because  they  are  not  as  heat-resisting  as  Classes 
"B"  and  "G." 


PLATE  XII 


ILLUSTRATIONS  159 


Plate  No.  XII. 

TERMINAL    BUSHINGS,    CONTACT    PARTS,    ETC.,    REQUIR- 
ING   HIGH    HEAT-RESISTING    QUALITIES 


The  majority  of  these  pieces  are  used  to  insulate  contacts 
of  electric  flat  irons  or  other  heating  appliances,  and,  being 
permanently  located  inside  of  the  latter  or  even  attached  directly 
to  the  heating  element,  must  necessarily  stand  continuous  high 
temperatures,  the  minimum  requirement  being  800°  C. 

While  the  ceramic  materials  of  Class  "~D'  would  stand  the 
heat  required,  .they  have  been  little  used  for  this  purpose,  due 
to  the  impossibility  of  molding  metal  contacts  in  place,  and 
the  attainment  of  the  required  degree  of  accuracy  to  insure  a 
proper  fit  between  the  male  and  female  contacts. 

Materials  of  Class  "A"  are,  of  course,  entirely  unsuitable, 
while  those  of  Classes  "E"  and  "G,"  and  even  Class  "B,"  are 
not  sufficiently  heat-resisting. 

The  only  remaining  available  materials  are  those  of  Class 
*'G"  which,  when  made  with  a  proper  regard  for  the  heat 
conditions  to  be  met,  are  entirely  suitable  and  almost  exclusively 
adopted  for  this  purpose. 


PLATE   XIII 


ILLUSTRATIONS  161 


Plate  No.   XIII. 

ARC    DEFLECTORS,     SEPARATORS    AND    SIMILAR    PIECES 

USED    IN   ELECTRIC    CONTROLLERS   AND    AUTOMATIC 

APPARATUS  SUBJECTED  TO  CONTINUOUS  ARCING 


By  referring  to  the  previous  treatment  of  this  subject,  it 
will  be  readily  understood  that  no  material  containing  organic 
substances  in  any  form  could  be  considered  for  this  purpose. 

The  only  suitable  materials,  therefore,  are  the  ceramics  of 
Class  "D,"  and  the  cold  molded  inorganic  products  of  class  "C."' 
The  latter  predominate,  however,  owing  to  their  mechanical  ad- 
vantages, porcelain  being  used  only  in  a  few  instances. 


PLATE  XIV 


ILLUSTRATIONS  163 


Plate  No.  XIV. 

RAILROAD  THIRD  RAIL  AND  SIGNAL  PARTS 


Figures  A,  B,  C  and  D  illustrate  a  series  of  third  rail 
insulators  for  service  on  the  regular  660  volt  circuit. 

Figures  C  and  D  are  satisfactorily  produced  in  the  materials 
of  Classes  "A,"  "B,»  "C,"  "D"  and  "G,"  though  the 
ceramics  predominate  at  the  present  time  owing  to  their  low 
cost.  Figures  A  and  D  can  only  be  produced  in  the  materials 
of  Classes  "A,"  "B,"  "C"  and  "G,"  owing  to  the  heavy 
metal  parts  which  are  molded  in  place. 

As  regards  suitability,  it  is  generally  accepted  that  the 
ceramics  are  superior  regarding  their  dielectric  and  physical 
attributes,  while  the  products  of  Classes  "A,"  "B,"  "C" 
and  "G"  are  superior  mechanically. 

The  essentials  are  dielectric  and  mechanical  stability  under 
long  term  of  service  in  all  weather  conditions;  these  have 
been- successfully  met  by  materials  of  Classes  "B,"  "C"  and 
"G"  under  observation  for  four  years  in  actual  use.. 

The  ceramics,  though  satisfactory  in  every  other  respect 
and  lower  in  cost,  are  liable  to  excessive  breakage. 

The  other  parts  shown  in  this  cut,  used  in  electric  signaling 
apparatus,  are  now  made  in  materials  of  Classes  "G" 
or  "C.M  The  former  are  preferred  when  absolute  accuracy  is  re- 
quired, but  where  variations  of  from  5  to  10  thousandths  per 
inch  may  be  allowed,  the  materials  of  Classes  "B"  and  "C"  are 
-very  suitable. 

Materials  of  Classes  "A"  and  "E';  are  rarely  used  for  such 
purposes. 


I 


PLATE  XV 


ILLUSTRATIONS  165 


Plate   No.   XV. 

MOLDED   BASES   AND    COVERS 


Hitherto,  such  parts  have  been  cut  from  slate  and  fibre, 
but  more  recently  there  has  been  a  very  distinct  tendency  in 
favor  of  molded  materials  with  the  preference  given,  to  pro- 
ducts of  Classes  "C"  or  "G,"  and  to  a  lesser  degree,  Classes 
11  A"  and  "B."  Accurate  molding  and  low  cost,  as  well  as 
dielectric  and  mechanical  suitability  have  placed  materials  of 
Class  "C"  in  the  lead,  while  Class  "G"  has  served  for  special 
purposes.  . 

The  ceramics  of  Class  "DM  are  not  as  suitable,  owing  to 
the  difficulty  of  obtaining  perfectly  flat  surfaces. 


o 


O  j,  O 

I^BW^^H^^^^^K 


PLATE  XVI 


ILLUSTRATIONS  167 


Plate  No.  XVI. 

SPECIAL    MOLDED    PARTS    USED    IN    CONNECTION    WITH 
ELECTRIC  MOTORS,   FANS  AND  APPLIANCES 


Materials  of  Classes  "B,"  "C"  and  "G"  are  the  most 
suitable  for  such  parts,  as  the  apparatus  in  which  they  are 
used,  is,  at  times,  liable  to  overheating  and  it  is,  therefore,  impor- 
tant that  the  insulation  used  should  stand  temperatures  of  not  less 
than  100°  C.,  without  softening. 

Materials  of  Class  "D"  are  used,  owing  to  their  low  cost, 
but  are  gradually  being  superseded,  owing  to  the  greater  accuracy 
and  better  mechanical  features  obtained  with  materials  of  the 
other  classes. 

Materials  of  Class  "G"  can  be  molded  in  such  shapes 
with  absolute  accuracy,  while  materials  of  Classes  "B"  and  "C" 
require  a  variation  allowance  of  a  few  thousandths  per  inch. 


PLATE   XVII 


ILLUSTRATIONS  169 


Plate  No.  XVII. 

SWITCH  BASES,   COVERS  AND  RECEPTACLES 


Ten  years  ago  porcelain  was  the  only  material  used  for 
these  bases  and  receptacles,  while  the  covers  were  made  of 
Class  "A,"  or  more  often  of  stamped  metal  lined  with  insulating 
paper  or  fibre. 

Since  that  time,  however,  the  introduction  of  materials  of 
Class  "B"  has  opened  a  wider  choice  to  designers,  and  many 
are  availing  themselves  of  the  advantages  to  be  obtained  from 
the  use  of  these  products. 

Materials  of  Class  "B"  have,  in  fact,  been  found  satisfactory 
for  receptacles,  bases,  and  covers,  permitting  of  the  production 
of  complete  assembled  parts  in  the  same  material. 

Tn  European  countries,  there  has  been  a  very  marked  move- 
ment in  favor  of  materials  of  Class  "B"  for  the  production  of 
these  parts,  while  in  the  United  States  the  tendency,  though  more 
gradual,  would  seem  to  indicate  their  favorable  consideration 
among  many  of  the  leading  manufacturers  of  electrical  ap- 
pliances. 

The  designer  may,  therefore,  safely  follow  his  own  judgment, 
selecting  materials  of  Class  "D"  if  he  desires  to  be  conservative 
and  follow  in  the  lines  of  established  practice,  or  by  selecting 
materials  of  Class  "B"  if  he  desires  to  avail  himself  of  the 
greater  accuracy  and  consequent  reduced  assembly  difficulties 
offered. 


PLATE  XVIII 


ILLUSTRATIONS  171 


Plate  No.  XVIII. 

ATTACHMENT   PLUGS   AND   PARTS 


Until  very  recently  these  parts  have  been  made  of  porcelain r 
or  where  a  tougher  material  was  required,  of  Class  "A"  pro- 
ducts. At  present,  however,  materials  of  Class  "B"  offering,  as- 
they  do,  the  heat-resisting  qualities  of  porcelain  with  the  tough- 
ness of  Class  "A"  products,  are  also  very  extensively  used. 

To  a  limited  extent,  owing  to  their  comparatively  high 
cost,  materials  of  Classes  "G"  and  "E"  are  also  used. 

In  fact,  the  choice  between  Class  "D"  and  Class  "B"  ma- 
terials would  seem  to  be  a  matter  of  individual  preference,  both 
being  considered  satisfactory,  with  a  growing  tendency  in  favor 
of  the  latter. 


172  MOLDED   INSULATION 


LABORATORY  TESTS 


In  describing  the  various  classes  of  molded  insulat- 
ing materials  and  their  properties,  relative  values  have 
been  considered  only  in  the  abstract,  while  in  the  chapter 
covering  the  selection  of  materials  and  illustrating  -typical 
molded  parts,  a  more  definite  attempt  has  been  made 
to  distinguish  between  the  classes,  and  to  establish  their 
individual  merits  for  specific  purposes  011  the  basis  of 
results  obtained  and  present  day  usage  in  the  electrical 
industry. 

As  far  as  possible,  reference  to  definite  laboratory 
tests  has  been  avoided,  as  liable  to  be  misleading,  partly 
due  to  a  want  of  standardized  methods  in  testing  molded 
insulating  materials,  but  principally  due  to  variations 
in  the  quality  of  raw  materials  and  methods  of  manu- 
facture. Practically  all  published  information  available, 
up  to  the  present,  has  been  obtained  from  manufac- 
turers of  the  various  molded  insulating  products,  or 
at  best,  from  tests  made  on  samples  furnished  for  this 
specific  purpose.  Comparisons  based  on  such  data  are 
seldom  conclusive  and  cannot,  therefore,  be  considered 
a  safe  guide  in  determining  the  most  suitable  insulat- 
ing product  to  be  specified  for  any  particular  purpose. 
In  fact,  it  is  generally  accepted,  among  electrical  engi- 
neers, that  they  must  depend  on  their  own  tests,  though 
Ihey  are  most  often  governed  by  the  more  practical  con- 


LABORATORY   TESTS  173 

sideration  of  length  of  service  and  reliability  established 
by  common  experience. 

Owing  to  their  scientific  and  general  interest,  how- 
ever, the  author  has  felt  that  laboratory  tests  should 
be  accorded  a  place  in  this  work. 

In  order  to  render  such  tests  as  nearly  as  possible 
comparative,  commercial  samples  of  the  more  generally 
manufactured  insulating  products  have  been  procured 
rather  than  special  samples  prepared  with  a  knowledge 
of  the  purpose  for  which  they  were  required. 

The  results  given  do  not,  therefore,  cover  all  of  the 
products  of  the  classes  of  materials  tested,  as  these 
would  show  wide  differences  due  to  variations  in  methods 
of  preparation,  quality  of  binders  and  fillers  used,  and 
conditions  of  manufacture.  It  follows  in  some  instances 
that,  as  has  already  been  stated,  the  reverse  of  con- 
clusions based  on  such  tests  would  hold  where  products, 
seemingly  inferior  under  the  laboratory  test,  would  prove 
superior  for  practical  purposes  of  service. 

In  the  tests  which  follow,  reference  has,  in  some 
cases,,  been  made  to  two  or  three  products  of  the  same 
class  indicated  by  the  letters  a,  b,  etc.  This  has  been 
done  to  demonstrate  the  wide  range  of  results  that  may 
be  obtained  from  different  commercial  products  manu- 
factured on  the  same  general  principle  and  in  the  same 
class  of  material. 

Materials  of  Classes  "D,"  "B,"  "F,"  "H"  and  "I" 
being  more  generally  known  and  understood,  it  has  not 
been  thought  necessary  to  give  them  a  place  in  these 
tests  which  are  confined  to  the  more  recently  introduced 
materials  of  Classes  "A,"  "B,"  "C"  and  "G." 

All  of  the  figures  given  have  been  prepared  under 
the  personal  supervision  of  Mr.  F.  M.  Farmer,  of  the 


174  MOLDED    INSULATION 

Electrical  Testing  Laboratories  of  New  York. 

In  some  cases,  the  form  of  test  has  been  suggested 
by  the  author  to,  as  nearly  as  possible,  approach  prac- 
tical conditions  as  met  in  his  own  experience. 


DIELECTRIC   STRENGTH   TESTS  175 


DIELECTRIC  STRENGTH  TESTS 


These  tests  were  made  with  samples  of  the  following 
shapes  and  obtained  as  follows : 

Class  "A."     Plates  2%"xl7s"xi/2"  cut  from  molded 
plates  6"x4:"xy:>". 

Class  "A"  (a).    Molded  bushing,  irregular  shape,  3"x 
2%"   over  all. 

Class  "B."     Cover,  over  all,   dimension  2%"x2%"x 
1%"  high,  width,  i/2"  wall. 

Class  "B"  (a).     Caps  for  hexagonal  nuts  or  bolts, 
maximum  width  of  head,  1",  thickness  of  wall,  %". 

Class  "C."     Plates  3}i"x2%wx5/16"  thick,  cut  from 
one  plate  5"x7"x5/16". 

Class  "C"  (a).     Plates  3"x3"x%"  cut  from  one  plate 

7"x7"x%". 

Class  "G."     Plates  4"x2%"x%"  cut  from  one  plate 
8"x6"xV2". 

Class   "G"(a).      Plates   4"x2%"xi/2"    cut    from    one 
sheet  8"x8"xy2". 

Class  "G"  (b).     Molded  bushing  l%irxl%w  over  all. 


The  dielectric  strength  tests  were  made  with  the 
sample  placed  between  blunt  needle  points;  voltage  was 
applied  to  the  needle  points  at  a  low  value,  and  gradually 


176  MOLDED    INSULATION 

increased,  until  puncture  occurred.  The  high  tension 
voltage  was  measured  by  means  of  a  voltmeter  connected 
across  the  low  tension  winding  of  the  transformer,  the 
ratio  being  known.  The  current  was  obtained  from  a 
60  cycle  course,  the  wave  form  of  which  is  practically  a 
sine  curve. 


TESTS 


177 


SAMPLE  TESTED  AS  RECEIVED 


Class  "A"  Specimen  No.  1 

Specimen  No.  2 
Specimen  No.  3 

Class  "A"  (a)  Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

Class  "B"  Specimen  No.  1 

Specimen  No.  2 
Specimen  No.  3 

Class  "B"  (a)  Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

Class  "C"  Specimen  No.  1 

Specimen  No.  2 
Specimen  No.  3 

Class  "G"  Specimen  No.  1 

Specimen  No.  2 
Specimen  No.  3 

Class  "G"  (a)  Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

Class  "G"  (b)  Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 


Volts    Per    Mil. 
152 

17S 
143 

361 
350 
353 

91.8 
83.5 
88.0 

167.0 
148.7 

i59.a 

69.5 
72  ^ 
70.8 

46.2 
41.7 
45.0 

221 
213 
218 

326 
315 
333 


178 


MOLDED    INSULATION 


SAMPLES  TESTED  AFTER  IMMERSION  IN  WATER  TOR  72 

HOURS 


Class 


Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 


Class  "A"  (a)  Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 


Class  <'B 


Class  "B 


Class  "C" 


Class  "G> 


Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

(a)  Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

Specimen  No'.  1 
Specimen  No.  2 
Specimen  No.  3 

(b)  Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 


Volts  Per  Mil. 
114 
110 
103 

287 
293 
301 

53 

58 
55 

121 
118 
107 

42 
40 
45 

40 

'  36 

38 

235 

228 
241 


TESTS 


179 


SAMPLES  TESTED  AFTER  IMMERSION  IN  TRANSFORMER 
OIL  AT  75°  C.  FOR  72  HOURS 


Volts    Per    Mil. 

^Class  "A" 

Specimen  No.   1 

152 

Specimen  No.  2 

170 

Specimen  No.  3 

1C4 

Class  "B" 

Specimen  No.   1 

193 

Specimen  No.  2 

169 

• 

Specimen  No.  3 

188 

Class  "C" 

Specimen  No.   1 

145 

Specimen  No.  2 

149 

Specimen  No.  3 

147 

• 

\ 

Class  "G" 

Specimen  No.  1 

30.3 

. 

Specimen  No.  2 

29.8 

Specimen  No.  3 

31.0 

Class  <-'G"   (a) 

Specimen  No.   1 

180 

Specimen  No.  2 

184 

Specimen  No.  3 

180 

*NOTE — Samples    blistered   and   were    slightly   deformed   after   test. 


180 


MOLDED    INSULATION 


SAMPLESJTESTED    AFTER    SUBJECTION    TO  ^ 
TURE  OF  100°  C.  FOR  12  HOURS 


TEMPERA- 


'Class "A 


Class  "B 


Class 


Class  "G 


Class 


(a) 


Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 


Volts  Per  Mil. 
87.7 
91.1 
86.0 

90.0 
84.0 
91.0 

70.0 
730 


65.7 
67.0 
63.0 

163.5 
159.6 
166.0 


*XOTE — Samples    blistered    and   were    slightly   deformed    after   test. 


TESTS 


181 


SAMPLES    TESTED    AFTER    SUBJECTION    TO    A   TEMPERA- 
TURE OF  200°  C.  FOR  12  HOURS 


*Class  "A 


Class 


Class 


Class 


^Class  "G 


Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 


Volts  Per  Mil. 
67.0 
60.0 
62.0 

98.0 

10S.O 

96.0 

74.0 
79.0 
76.0 

102.5 
109.0 

iui.o 

119.0 
116.0' 
1240 


^NOTE — Samples  were  swollen  up  after  test  and  entirely  deformed. 
— Samples   were    blistered   and    slightly   deformed   after    test. 


182  MOLDED    INSULATION 


SAMPLES    TESTED    AFTER    SUBJECTION    TO    A  TEMPERA- 
TURE OF  300°   C.  FOR  12  HOURS 

Volts  per  Mil. 
*Class  "A"  Specimen  Xo.  1 

Specimen  No.  2  ... 
Specimen  No.  3 

Class  "B"               Specimen  No.  1  96 

Specimen  No.  2  105 

Specimen  No.  3  102 

Class  "C"                Specimen  No.   1  94 

Specimen  No.  2                 ,  90 

Specimen  No.  3  96 

*Class  "G"  Specimen  No.  1 

Specimen  No.  2  ... 

Specimen  No.  3  ... 

*Class  "G"   (a)       Specimen  No.  1 

Spe'cimen  No.  2  ... 

Specimen  No.  3  ... 

*NOTE — Unable    to    test    because    of    change    caused  by    heat. 


TESTS 


183 


SAMPLES    TESTED    AFTEE    SUBJECTION    TO    A    TEMPERA- 
TURE   OF    300°    C.,    COOLING    AND    THEN    SUBJECTING    TO 
IMMERSION   IN  WATER  FOR  24  HOURS 


f  Class 


Class  "B 


Class 


^Class  "G 


*Class 


(a) 


Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 


Volts  per  Mil. 


80 

78 
83 

55 
57 
54 


'NOTE — Not   tested    because    of   change    caused   by    heat. 


184  MOLDED    INSULATION 


INSULATION   RESISTANCE    TESTS 


The  samples  submitted  for  this  test  were  the  same  as  those 
used  for  the  puncturing  tests.  They  were  first  used  for  measure- 
ments of  the-  resistance,  and  afterwards  for  the  puncture  tests. 

The  insulation  resistance  was  measured  by  the  usual  high 
sensibility  series  galvanometer  method,  the  time  of  electrification 
being  one  minute.  Voltage  of  150  and  700  volts  were  employed, 
depending  upon  the  value  of  insulation  resistance  to  be  measured. 
The  electrodes  employed  were  containers.  A  guard  ring  was 
employed  so  that  the  question  of  surface  leakage  was  thereby 
eliminated. 

When  the  immersed  samples  were  withdrawn  from  the  water, 
the  excess  surface  moisture  was  removed  with  blotting  paper. 
Since  the  samples  were  very  small  and  the  guard  ring  near  the 
edge,  it  is  probable  that  the  leakage  current  was  relatively  large 
and  the  result  must  be  considered  of  questionable  value. 


TESTS  185 


SAMPLES   TESTED  AS  RECEIVED 

Insulation  resiatance  megohms 
per  inch,  cube 

Class  "A"  Specimen  No.  1  235,710 

Specimen  No.  2  60,700 

Specimen  No.  3  174,200 

Class  "A"   (a)       Specimen  No.  1  Greater  than    1,000,000 
Specimen  No.  2        "  "      1,000,000 


Class  "-B" 

Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

21,300 
18,070 
12,300 

Class  "B"   (a) 

Specimen  No.  1 
Specimen  No.  2 

51,200 
40,700 

Class  "0" 

Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

290,000 
115,000 
240,000 

Class  "C"   (a) 

Specimen  No.  1 
Specimen  No.  2 

24,900 
28,100 

Class  "G" 

Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

•     65 
93 
76 

186 


MOLDED    INSULATION 


SAMPLES  TESTED  AFTER  IMMERSION  IN  WATER  FOR  72 

HOURS 


Insulation  resistance  megohms 
per  inch,  cube 


Class  "A" 

Specimen  No.   1 
Specimen  No.  2 
Specimen  No.  3 

513 
890 
1070 

Class  "A"   (a) 

Specimen  No.   1 
Specimen  No.  2 

800,000 
600,000 

Class  "B" 

Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

470 
380 
710 

Class  "B"   (a) 

Specimen  No.  1 
Specimen  No.  2 

14,300 
17,210 

Class  J'O" 

Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

900 
1,320 
1,150 

Class  "0"   (a) 

Specimen  No.  1 
Specimen  No.  2 

21,110 
19,000 

Class  "G" 

Specimen  No.  1 

51.0 

Specimen  No.  2 
Specimen  No.  3 

40.0 
42.0 

Class  "G"   (a) 

Specimen  No.   1 
Specimen  No.  2 
Specimen  No.  3 

7,590 
11,400 
8,100 

Class  "G"   (b) 

Specimen  No.  1 
Specimen  No.  2 

6,250 
5,600 

TESTS 


187 


SAMPLES    TESTED    AFTER    SUBJECTION    TO    A    TEMPERA- 
TURE OF  100°  C.  FOR  12  HOURS 


* Class  "A" 


Class  "B>- 


Class 


Class 


Class  «G"  (a) 


Insulation  resistance  megohms 
per  inch,  cube 

Specimen  No.  1  Greater  than    1,000,000 
Specimen  No.  2      v"  "       1,000,000 

Specimen  No.  3        "  "       1,000,000 


Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 


25,800 
36,100 
30,400 


Specimen  No.   1  Greater  than    1,000,000 


Specimen  No.  2 
Specimen  No.  3 

Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 

Specimen  No.  1 
Specimen  No.  2 
Specimen  No.  3 


1,000,000 
1,000,000 

1,790 
2,310 
3,840 

250,000 
340,000 
376,000 


'NOTE — Samples    blistered    and    warped    slightly. 


188 


MOLDED    INSULATION 


SAMPLES    TESTED    AFTER    SUBJECTION    TO    A    TEMPERA- 
TURE OF  200=   C.  FOR  12  HOURS 


'Class  "A" 


Class  "B" 


Class  "0" 


'Class 


h*Class  "G"   (a) 


Insulation  resistance  megohms 
per  inch,  cube 

Specimen  Xo.  1  Greater  than    1,000,000( 
Specimen  No.  2        "  "      1,000,000 

Specimen  Xo.  3        "  "      1,000,000 


Specimen  XTo.  1 
Specimen  Xo.  2 
Specimen  XTo.  3 


350,000 
405,000 
341,000 


Specimen  Xo.  1  Greater  than    1,000,000 
Specimen  Xo.  2        lt  "      1,000,000 

Specimen  Xo.  3        "  "       1,000,000 


Specimen  Xo.  1 
Specimen  Xo.  2 
Specimen  No.  3 


850..000 
970,000 
680,000 


Specimen  Xo.  1  Greater  than    1,000,000 
Specimen  No.  2        "  "      1,000,000 

Specimen  No.  3        "  li      1,000,000 


*NOTE — Samples    blistered    and    swelled    badly. 
**NOTE — Samples     blistered     and     swelled     slightly. 


TESTS 


189 


TENSILE    STRENGTH    TESTS 

Samples  for  these  tests  were  submitted  in  the  form  of 
standard  briquettes  used  in  cement  testing.  These  briquettes 
were  cut  out  of  blocks  about  1"  thick  of  the  respective  materials. 

These  tests  were  made  in  a  standard  tensile  testing  machine 
having  a  capacity  of  4,000  Ibs.  The  jaws  employed  corresponded 
in  design  with  the  standard  shape  used  in  testing  cement  bri- 
quettes. 


SAMPLES   TESTED    AS   RECEIVED 


Tensile   strength.pounds  per   square  inch 


Class  "A" 


Class  "B 


Class 


Class  "G 


Class  "G"  (a) 


Specimen  No.  1 
Specimen  Xo.  2 
Specimen  Xo.  3 
Specimen  Xo.  4 

Specimen  Xo.  1 
Specimen  Xo.  2 
Specimen  No.  3 
Specimen  Xo.  4 

Specimen  Xo.  1 
Specimen  Xo.  2 
Specimen  XTo.  3 
Specimen  Xo.  4 

Specimen  Xo.  1 

Specimen  Xo.  2 

•  Specimen  Xo.  3 

Specimen  Xo.  4 

Specimen  Xo.  1 
Specimen  Xo.  2 
Specimen  Xo.  3 
Specimen  Xo.  -4 


2,000 

940 

1,090 

1,010 

1,550 

920 

1,285 

1,421 

2,230 
1,985 

2,478 
2,918 

3,020 
4,000 
2,920 
3,405 

4,750 
3,780 

2,880 
3,860 


190  MOLDED   INSULATION 


ARC  TESTS 


The  following  samples  were   submitted  for   tests: 

Class  "B"  Molded   piece   of   irregular  shape   I%"x2%"x1/4l 

over   all. 


Class  "C>-  Molded  block  4%"x2%"x2%' 

Class  "C"  (a)      Molded   block   5"x3"x%". 

Class  "C"  (b)      Disc    4%"x%". 

Class  "G"  Block  3"xl"xl". 

Class  "G"  (a)     Block   2%"xl%"x%". 


TESTS  191 


TESTS 


(a)  Sample    held    ]/4"    above    the    flame    of    the    arc    for 
one    minute. 

(b)  Sample   passed    slowly   through    a   part   of   the    flame 
of  the   arc. 

(c)  Sample  held  in  the  flame  of  the  arc  for  one  minute. 

(d)  Sample  ignited,  when  possible,  and  then  held  in  the 
open    air. 

(e)  Sample    carbonized    when    possible,    and    held    across 
the    extinguished   arc,    carbons   still   hot,   to   re-estab- 
lish   arc. 

(f)     Same  as  test  "e,"  except  carbons  were  first  allowed 
to  cool. 


192  MOLDED    INSULATION 


RESULTS  OF   TESTS 


Class  "B" 

Test  Result 


a.  Became  red  hot  and  charred  slightly. 

b.  Charred,  but   did   not   catch   fire. 

c.  Became  red  hot  and  charred. 

d.  Became   red  hot,   would  not   burn. 

e.  When   carbonized  was   conducting. 

f.  When   carbonized   was   conducting. 


Class   "C" 

Test  Result 


a.  No    noticeable    effect. 

b.  Fused    quickly    to    a    glass-like    sub- 
stance. 

c.  Fused    slowly. 

d.  Would    not    burn. 

e.  Non-combustible     and     non-conduct- 
ing. 

f.  Non-combustible     and     non-conduct- 
ing. 


Class   "C"  (a) 

Test  Result 


a.  No    noticeable    effect. 

b.  Fused    slowly. 
C.     -   Fused  slowly. 

d.  Would    not   burn. 

e.  Non-combustible     and     non-conduct- 
ing. 

f.  Non-combustible     and     non-conduct- 
ing. 


Class  "G"  (b) 


TESTS 


193 


Test  Result 

a.  Charred  slightly. 

b.  Caught    fire    slowly. 

c.  Caught  fire  and  fused. 

d.  Would   not   burn    outside   of   arc. 

e.  Fused    portion    was    conducting. 

f.  Fused    portion    was    non-conducting. 


Class  "G 


Test  Result 

a.  Caught    fire    slowly. 

b.  Caught  fire,  but  stopped  on  leaving 
arc. 

c.  Caught    fire    and    burned    in    air    a 
little. 

d.  Caught    fire    and    burned    in    air    a 
little. 

e.  Charred    and    became    conducting. 

f.  Charred    and    became    conducting. 


Class    "G"  (a) 


Test  Result 

a.  Caught    fire    instantly. 

b.  Caught   fire   and    continued   to   bum. 

c.  Caught  fire  and  charred. 

d.  Caught  fire  and  burned  for  about  1. 
minute. 

e.  Charred   and  became   conducting. 


INDEX. 


195 


Abrasive  action   32 

1 '         wheels   109 

Accuracy,  18,  72,  89,  97,  119, 
125,  13"4,  151,  159, 
163,  165,  167,  169 

Acetaldehyde    64 

Acetone 44,  64 

Acetylene    56 

Acids,  12,    21,    22,    40,    47,    60, 
6],   80,  82,  86,  107. 

11      acetic    62,  83 

' '       benzolsulphonic    ....    61 

' '       hydrochloric    13,  64 

1 '       nitric    34 

' '      nitrous    63 

' '       organic     64 

"      proof... 20,    21,   24,    107 
"      resisting     qualities,     21, 
22,  107. 

1 '       sulphonic   61 

"       sulphuric,  13,  31,  61,  63, 

64,  80,  81,  83,  90. 
Adhesive   qualities,   25,   26,   53 

Adulterants 42,  49,  50 

Africa    21,   43,  52 

Air    22,  81,  191 

Albumin    60,  62,  95 

Alcohol,  42,  44,  51,  53,  57,  60, 
62,  80. 

Aldehyde. . 56,   57,   59,  64 

Alkalies 13,  21,  40,  47,  64, 

107. 

' '       caustic  ...  .83 


Alkaline     agents 86 

compounds     90 

' '          earths 30 

silicate    76,  77 

Alumina,  21,  23,  24,  26,  27,  29, 

34,  73. 
Aluminous  materials.  ..  .10,  30 

Aluminum   silicate 24 

Amazon  tree .  : 52 

Amber    59,  83 

Amboyna  pine 45 

Ammonia   59,  63,  64 

Amperages     155 

Amphibole   20 

Amylalcohol 56 

Aniline    64 

Anhydrides    64 

Animal    oil    39 

Animal   products 41 

Antophyllite .   20 

Apparatus    85,  121,  161 

Appearance,  19,  31,  32,  34,  37, 
44,  68,  69,  71,  74, 
79,  88,  102,  108, 
109,  110,  125,  127, 
129,  139,  141,  143, 
155. 

Arc  deflectors    106,  161 

11    electric,  22,  74,  88,  91,  104r 
106,   107,  191. 

"    tests    190 

Arcing    89,  106,  161 

Aromatic    compounds 60 

Artificial    stone.  .  .   31 


196 


MOLDED    INSULATION 


Asbestos,  9,  10,  20,  21,  22,  25, 

26,  31,  32,  55,  58,  66, 

68,  71,  72,  73,  74,  78. 

.   .  88,   89,   103,   157. 

1 '          compounds     .....    22 

' '          vulcanized   9 

Asia    37,   41,  52 

Asphalt,  10,  13,  17,  38,  39,  40, 
42,  43,  48,  49,  50,  51, 
66,  68,  71.  ' 

' '         artificial 39 

'  <         lakes    39 

' '         natural    39 

« '         petroleum    39 

Assembling   difficulties 169 

Atmospheric   condition 95 

"  exposure,    46,  50, 

91. 

Atomic    combination 87 

Attachment    plugs 171 

Austria   38 

Automobile  work 132,  134 


Barbadoes    39 

Barrier   130 

Bases    128,  165 

Basket    38 

Belgium    38 

Benzaldehyde    64 

Benzene   51,  60 

Benzine    44,  46,  51 

Benzol 44,  46,  51,  59,  62 

Benzoline     51 

Billiard  'balls 31 

Binders,  7,  9,  10,  12,  14,  15,  16, 
20,  22,  25,  30,  31,  32. 
33,  40,  42,  46,  49,  66, 
67,  68,  69,  71,  72,  73, 
74,  78,  85,  88,  89,  91, 
92,  99,  103,  107,  173 


Binders,  asphaltic    15 

1 '         fireproof     26 

"         heat  resisting 11 

"         hydraulic    74 

"         inorganic,   26,   30,    33, 

73,  74. 

"         organic,  7,  16,  21,  22, 
32,  66,  69,  71,  73,  74, 
'  84,  89,  106. 

"         resinous,  15,  24,  90,  92 
1 '         synthetic,    84,    85,  88, 
89,  91,  99. 

Binding   value    33 

Bismuth    59 

Bitumens 39,  40,  68,  69 

Bituminous    substances....    38 

Blast  furnace  slag 30 

Blistering,    179,    180,    181,  187, 
188. 

Blocks 79,  80,  130,  189,  190 

Blood 11 

Bobbins    14 

Bone  59,  60 

Box,  fuse    122 

"       insulating.  .120,   121,  122 

' '      switch    122 

Breakage    163 

Bricks  28 

Brittleness 9,  40,  101,  155 

Bromine   water 63 

Buffalo    28 

Buffing    109 

Burning 29,  30,  104,  192 

Burrs    Ill,  116,  127 

Bushing   116,  175 

Buttons    .  .    12 


Calcination   27,  28 

Calcium  acetate   .  .   64 


INDEX 


197 


Calcium  aluminates    30 

"  bisulphite    35 

' '  carbonate 27,  64 

"  chlorate    13 

' '  chlorides    31 

1 '  salts    64 

tl  silicates 30,  33 

1 '  sulf ate    26 

Camphor,  33,  34,  35,  79,  80,  81, 

82. 

"          oil    34 

"          synthetic    35 

Camphoric   acid 35 

Canada    20,  21,  23 

"         dept.   of   mines 20 

Caimabis   sativa 37 

Caoutchouc    52,  78,  83 

Carbolic    acid 60,  88 

Carbon    38 

"          bisulfide    44,  62 

''<          dioxide    27,  31 

Carbonate  of  lime 30 

Carbonic    acid 58 

Carbonizing    191,  192 

Carborundum    109 

Carteria    lacca 41 

Casein    12,  83,  84,  104 

Catalyser '.57,  58 

Catalytic    nature 73,  86- 

Caustic  alcali 83 

Caustic  soda 35 

Celluloid,  14,    35,    37,    79,    81, 

82,   83,   104. 
Cellulose.  14,  33,  49,  79,  80,  81, 

94. 

Cement,  26,  27,  28,  29,   30,  31, 
73,  120. 

"        briquettes     189 

"        rock .    29 

"        testing     189 

•Cementing  media 


Central   America 52 

Centrifuges    80 

Ceramics,  16,  72,  75,  93,  104, 
107,  120,  128,  134, 
139,  141,  143,  151, 
155,  157,  161,  163, 
165. 

Ceresin   wax 40 

Chalk    30,  75 

Charcoal    34,  42 

Charring 104,  106,  155,  192 

Chemical  action   93 

analysis    20,  71 

compounds    90 

China   33,  50 

Chinese    wood    oil 50 

Chipping 155 

Chlorides 31 

Chloroform 44,  53,  54,  62 

Chromates    14 

Classification   16 

Clay 22,  23,  28,  29,  30 

' '       china 75,  76 

' '      fused    75 

1 '       matter   . : 27 

Climatic  action     31 

"          conditions,  18,  22,  42, 
45,  68,  83,  95,  132. 

Closed  dies Ill,  112,  114 

Coal   28,  -29,  40,  61 

Coal  tar 39,  51,  50,  61,  62 

' '       "    colors    42 

"      "   pitch    39 

"       "   residues    39 

Column    dephlegmators.  . .  .   58 

Color,   44,   71,   79,   81,   82,    108, 
109. 

Coccus    lacca 41 

Components,  basic 30 

Condensation,  11,  60,  63,  64,  86, 

87. 


198 


MOLDED    INSULATION 


Condensation  products,   60,    65, 

86. 
process,  63,  65,  86 

Conducting 192 

Contacts   159 

Copal 43,  44,  45,  51,  91 

"     resins   40 

Copper   57,  58 

Coral   83 

Cotton    36,  37,  32,  80 

"       bags   42 

Counterbored    holes...  128,  130 
Cover,  insulating,  120,  121,  122, 
151,  165,  169, 
175. 

Cracking 155 

Cresol    62 

Crotonaldehyde    64 

Crude  rubber 52,  54,  55 

Crystalline    minerals 20 

Crystallization    35 

Cuba    ;   39 

Current    176,'  184 


Damar  Gum    45,  66,  68 

Decomposition    49,  82 

Deforming    102 

Dental  work 31 

Design 102,  108,  119 

Design,  ideal 123 

"        incorrect    125 

Deterioration    103 

Dextrine 15 

Diamidotriphenylmethan.  .  .  64 
Dielectric  strength,  9,  11,  24, 
25,  40,  45, 
55,  60,  91, 
93,  98,  99, 
102,  103, 
139,  153, 
163,  165, 
175. 


Dies,  7,  10,  11,  12,  13,  14,  16, 
17,  32,  66,  67,  72,  73,  74, 
76,  83,  87,  88,  95,  100, 
108,  109,  110,  111,  112, 
113,  116,  118,  132,  149 

"      closed Ill,     112,  114 

11     open   Ill,  112 

Dimethylamin   59 

Dinaphthol ' 64 

Discs    112,  190 

Disintegration   10,  102 

Dissolving  properties 51 

Distillation    34,  44 

Distorting    134 

Draw   123,  129,  130 

Drawings    97 

Driers 48 

Drilling 100 

Drums,    rotating 76 

Drying  oils 49,  50 

li       process    71 

1 '        qualities    50 

Durability    31 

Dye    42 

11     stuffs 59,  66,  79 


Eau  De  Javelle  ...........    63 

Ebonite   ...............  55,  83 

Ebony   ...................    83 

Efficiency    ................  110 

Egypt   .................  36,  39 

Elasticity.  .35,   54,   78,   82,  101 
Electrical    apparatus.  ..  .7,  105 

"  appliances   .....     7 

Electric    controllers  ........  161 

fans  .............  167 

"         motors    ..........  167 

"         signaling        appar- 

atus   ...........  163 

Electrical    Testing    Labora- 


174 


INDEX 


199 


Electrified    82 

Emery  wheels 31 

Engines,  hot .  132 

England    12 

Ether 44,  46,   62,  81,  82 

Ethyl  alcohol 51 

Ethylene 56 

Europe 5,  12,  37,  153 

Evaporative   qualities 50 

Expansion    153 


Fans,  electric 167 

Fats  39 

Feldspar 25,  30,  75 

Ferrichloride    63,  64 

Ferrous  oxide 21 

Fibre,  7,  9,  22,  32,  35,  36,  37,  38 
90,  91,  95,  99,  100,  101, 
104,  106,  130,  153,  155, 
165,  169. 

Fibre  products 17,  90,  100 

11      vulcanized    90,  155 

Fibrine 11,  12 

Fibrous  substances 87 

"        sheets    91 

Fig  trees 41 

Filler,  7.  9,  10,   12,   14,   16,  21, 

25,  31,  33,  35,  37,  66,  67,- 

68,  69,  71,  72,  73,  74,  87, 

88,  98,  99,  103,  105,  173 

"        inorganic,  16,     17,     31, 

55,     71,     78, 

83,     87,     89, 

106. 

11       organic,  31,  71,  78,  83, 
87,  89. 

Finishing 141,  143 

Finishing  treatment 116 

Fins    Ill,  127 

Fireproof   18,  20,  104 


Fireproof   coating 26 

Fireproof    material 9 

Fire  resisting 85 

Fire-resisting  qualities 22 

Fire   Underwriters 153 

Firing... 23,  72,  76,  77,  96 

Fixtures,   lighting 105 

Flames 82,  88,  91,  104,  191 

Flat   irons 159 

Flax 32,  37,  38,  48,  80 

Flexibility,  22,   24,    32,    35,  78, 
101. 

Flint    23,  25,  31 

Floorings    31 

Florida 22,  36 

Flowing    qualities 128 

Fluxes    23,  75 

Flux   material 25 

Fluxing    action 30 

Formaldehyde,  11,    14,    56,  57, 

58,    59,    60,  63. 

65,    83,    86. 

Formalin    57,  58,  59 

Formic    acid 56,  57,  58 

Formosa   . 34 

Fossil  gums 43 

France    38 

Fusing    106,  192 

Fuse  box 122 

Fusible   solid 86 

Fusing  point. 17 


G 

Gabon    44 

Galvanometer    184 

Gasoline  vapors 132,  133 

Genus   gossypium 36 

Georgia 36 

Germany   38,  153 


200 


MOLDED    INSULATION 


Glass    75,  82 

Glass-like  substances 192 

Glazing  108 

Glue,    animal 14 

"      cabinet   makers...  14,  59 
Glutinous   substances..  .  .12,  13 

Glycerine   62 

Grain  alcohol 51 

Grinding 120 

Grinding  machinery 29 

Guard   ring 184 

Gums,  10,   43,   44,    59,    68,    103 

1 '       alcohol  soluble 52 

' '       resinous     94 

Gun   cotton 79,  81,  82 

Gutta   percha 17 

Gypsum 75 


Hardness 75,  82,  40,  44 

Hard  rubber,  5,  7,  9,  12,  54,  55, 
59,  9ft,  100,  103, 
107,  109. 

Heat  resisting,  39,  41,  43,  45, 
47,  49,  55,  78, 
79,  84,  85,  86, 
88,  89,  91,  92, 
95,  101,  103, 
107,  122,  145, 
147,  149,  .  155, 
157,  159,  171 
"  "  qualities,  11, 

12,  15,  24,  25, 
30,  40,  45,  48, 
70,  79,  95. 

Heated  press  table 114 

Heating   appliances 159 

' '        elements 159 

Heatproof,  83,  88,  89.  91,  104, 

105,  133. 
Hemp    32,  37,  80 


Hevea,  plant 52 

Hexamethylene-tetra-amine.  59 

High  finish    145 

"      polish..  109,  116,  119,  145 

"      tension .70,  98,  176 

Holes,   counterbored..  .128,  130, 
Homogeneity,  76,  80,  90,  98,  99 

Hoof 12 

Hoof   products 49 

Horn 12,  83 

Horn    refuse 49 

Hot    engines 132 

"       oils    132 

Household  articles 157 

Hyatt  process 80 

Hydraulic 115 

cements,  10,  25,  26, 
27,  30,  31, 
33,  73. 

Hydrocarbon   47 

Hydroextractor 81 

Hydrogen 38,  58,  60,  64 

Hydrosiljcate  of  alumina.  .    25 
Hygroscopic 62,  68,  95,  104 


Ideal  design 123 

Igniting 82,  191 

Illinois    28 

Impregnating,    40,    45,    47,    48, 
50,    99. 

Inaccuracy 96 

Incorrect   design    125 

India 23,  39,  41 

Indiana     28 

"       rubber    56,  59 

Inflammability,  14,   70,   81,  82, 

83,  84,   85. 
Infusible    86,  87,  88 


INDEX 


201 


Insect    41 

Inserts,  118,  119,  121,  132,  134 

Insolubility    10,  82 

Insulated   knurls 125,  128 

Insulated   wires 151 

Insulating  'box,    120,    121,    122, 

151. 

Insulating  cloth,  40,  45,  48,  50 
tapes   ....40,  48,  50 

' '          value    7,  24,  99 

"  varnishes,  13,  40,  43, 

45,  50. 

Insulation,    resistance 184 

Insulator 78,    79,  102,  132 

Insulators,  resistance 77 

Iron    24,  58 

"      oxide,   23,   24,   26,   27,  29 

Isoprene 56 

Italy   20     i 


Japan    33 

' '        camphor    33 

Java   7 43,  45 


Kauri    : 44 

Kerosene  oil 59 

Ke£ones    64 

Kieselguhr 26 

Kiln    28,  30,  75,  76 

Knife 42 

Knurling,    126,  127 

"          braided    127 

"  straight    127 

Komppass  synthesis 35 

Kristallviolet    ,  .    59 


Laboratory  tests 173 

Lac 41,  42 

' '     crude    41 

"     button    • 42 

f  i     garnet 42 

< '     lake    42 

"     seed 42 

"     stick 41 

Lamp    black 66 

Lapis 83 

Laurus  camphora 34 

Lava    76 

Lavite    75,  105 

Lettering    .120 

Lighting  fixtures 105 

Lime,  21,  23,  26,  29,  30,  34,  39, 
66,  73. 

11       compounds  10,  33 

Limestone.  .  .23,  27,  28,  29,  30 

Lime   water 59 

Linaceae    38 

Linoxen   48,  49 

Linseed    oil 48,  49,  50 

"  "   boiled    48 

Lint 36 

Lirium  Usitatissimum ......    38 

Literature  11,  86 

Litmus    62 

Low  tension 72,  176 

M 

Machining   130 

Magnesia,  21,    23,    24,    26,    30, 
31,    66,    71,    73. 

"          cements    31,  33 

"  compounds     ..31,  33 

Magnesium  carbonate   .  .  27,  30 

"  chloride   31 

"  oxide    .  .   24 


202 


MOLDED    INSULATION 


Magnesium  oxychloride.  ...    31 
11          .silicate,    20,    24,  33 

Magneto  insulator 132 

Malachite     83 

Manganese 24 

Manilla 44 

Marble    7,  31,  83 

"        waste   14,  31 

Marl   29,  30 

Mechanical  advantages.  ..  .161 

' '  mixture 32 

stability,    163,    165, 

167. 
strength,  18,  19,  22. 

32. 

' '  suitability  ....  165 

Megohms.  .  .185,    186,    187,  188 

Melting  point,  35,    40,    42,  44, 

47,   62,   69,    107 

Mercury    59 

Mercury  bichloride 59 

Metal  contacts   159 

' '        covers   121 

inserts,  118,  120,  127,  147 

"        parts,  12,  21,  43,  97,  100. 

121,  130,  132,  134, 

141,  145,  151,  153, 

155,   157,   163, 

Metamorphosis 30 

Methan   58 

Methanal    56 

Methylalcohol.  .  .51,  56,  57,  58 

Methylaldehyde    56 

Methylenitan    59 

Mexico    39 

Mica,  7,  10,  23,  24,  25,  26,  42. 

92,  99. 
"       built-up,  24,  52,  91,  107 

1  <      flake 99 

' '      insulator    25 

"        molded 18,  92,  136 


refuse 


Micanite    segments 13H 

Milk,  curdled 83 

Mineral  fibre    15,   20,  32 

filler    14,  33 

."          oils    50,  61 

1 '          pitch    40 

11         substances 9 

Mines    21 

Mixing   machine 66,  67 

Moisture,  10,  12,  21,  22,  68, 
69,  72,  74,  83,  89, 
95,  102,  103,  104,  155. 
184. 

Molds,  7,   10,   11,   16,  110,   111, 
115,  117,  120,  125,  147. 

Mortar    33 

Motors,    electrical 167 

Mozambique    44 


N 

Naptha    51,  54 

Napthol. 64 

Natural    cements 28,  29 

Xeufuchsin    59 

New   York   Electrical  Test- 
ing Laboratories 174 

New  York  State 27 

New  Zealand 38,  43 

Nickel 58 

Nitric    acid ..80,  81,  83 

Nitro  cellulose... 35,  79,  80,  81 
«  "        industry  . .  .  .'  35 

Nitrogen    38,  79 

Non-absorbent    74 

Non-combustible     192 

Non-conducting    192 

Non-hygroscopic    68,  102 

Non-inflammable    84 

North    Carolina 36 

Numbering 120 


INDEX 


203 


Oil   9,  17,  24,  34,  45 

Oils,  hot 132 

Oil,  transformer 179 

Oil  vapors 132 

Oklahoma 37 

Open    dies Ill,  112 

Opening  material 25 

Orange   Shellac 42 

Organic  fibres 95 

material,  12,     25,     52, 
88,   98,   99. 

"        solvents  90 

Ovens    13 

Overheating    167 

Ox  blood    11 

Oxidation    57,  58 

Oxides 31 

Oxychloride   31 

Oxydizing  agents 48 

Oxygen 25,  48,  51,  64 

Ozokerite   .  .    40 


Papaver    somniferum 50 

Paper    13,  17,  90 

"        insulating 37,  169 

Paper    machine 10 

' '        tissue    80 

' l        satin    81 

Papier  mache 13 

Paraffine 14 

' '          hydrocarbons   ....   40 

11          wax 47 

Paraf ormaldehyde    57,  58 

Parafuchsin 59 


Patent    flooring 31 

1 '         literature    49 

Patents    11,  48 

Pennsylvania 28,  29 

Pestles    , 41 

Petroleum    50,  51 

Phenol,  11,   59,   60,   61,   62,   63, 
64,   65,   86. 

' '        formaldehyde,     36,     85, 

87,     89. 

Philippine   Islands 37,  43 

Photography   • 59 

Physical  attributes    163 

' '          changes    13,  33 

1 1          function     32 

' '          inertness    25 

qualities     139 

i '          structure    .  . 33 

Pigments 66,  79 

Pine    tree 46,  51 

Pins    116,  130 

Pitch    39,  40,  42,  66 

Plantation    rubber 53 

Plastic  binders 87,  88 

Plastic    mass 7 

11        material 73,  80,  82 

Plasticity,  73,  76,  81,  82,  87, 
88,  132. 

Plates 79,  175 

Plugs,  attachment 171 

Polish,  108,  109,  116,  119,  120, 
143,  143. 

Polymerization 56,    57,  58 

Porcelain,  22,  25,  30,  43,  70,  72, 
75,  76,  77,  93,  96,  98, 
99,  101,  104,  123, 
125,  139,  155,  161, 
169,  171. 

"  hard 75 

Portland  .  28 


204 


MOLDED   INSULATION 


Portland  cement,  23,  28,  29,  30, 
31,  73,  74. 

"         cement  mill 29 

"         stone   28 

Potash 23,  26,  62 

Potassium 24 

"  bisulphite   61 

Press    115,  117 

Press   table 1.14 

Properties    172 

1 '  chemical  68 

< '          dielectric   102 

< '          electrical    135 

"  insulating,     69,     72, 

98,   132, 
134. 
"  mechanical,  7,       74, 

135. 

"  molding    .  .  .11,  135 

physical,  7,  21,  45, 
54,  72,  74, 
78,  135. 

Proprietory  plasters 31 

Publication 20 

Punching    100 

Puncture   70,  98,  176,  184 

tests    97,  184 

Puzzolans 27 

Pyroxylin    .  .  .35,  81 


Quartz    25,  75 


Eaised  letters 120 

Eeceptacle    box 123,  169 

Eefractory  material 25 

Eeinf orcing   24 


Eesilient    100,  101 

"        artificial  86 

Besin— oils   44,  45 

Eesinous  binders,  11,  33,  24,  51 
-    "          bodies,  42,  43,  49,  48, 
51. 

' '          materials    87 

"          substance,  11,  12,  59, 
86,  91. 

nature    91 

Eesins,  13,  41,  42,  43,  44,  45, 
46,  48,  49,  50,  51,  52, 
64,  66. 

Eesistance  insulation    184 

"  insulators 106 

' '          test    184 

Bings    136 

Eiveting    100,  120 

Bock   27,  28,  29 

Bods   17,  79,  97,  136 

Boilers   41,  42,  53,  80 

"        calendering 81 

Bope    38 

Bosendale 27 

Eosin,  10,  42,  43,  46,  47,  50,  51, 
66,  68,  69. 

"        oil    49,  50 

'Eotary  kiln 29,  30 

Bubber,  9,  17,  40,  49,  52,  53, 
54,  55,  56,  78,  87,  89, 
94. 

1 '        artificial    56 

"  compounds,  17,  94,  98, 
101,  103,  105,  109,  131, 
132,  141,  143,  147,  155 

"  hard,  55,  99,   100,  103, 
107,  109. 

' '  substitutes  49,  55 

"  synthetic 56 

"  trees   52,  53 

' '  vulcanized    55 

Bussia  20,  38,  39 


INDEX 


205 


s 

Saccharine   substances 59 

Sample  pieces 110 

Sand 23,  25,  33,  66 

Sap 41,  46 

Saturating  qualities 40 

Saw  dust 31,  33 

Screw  heads    120 

"      holes    125 

Sea  island  cotton 36,  37 

Sealing  wax 43,  66,  120 

Secrecy 8 

Seed 36 

Separators,  arc 161 

Serpentine 20,  .21 

Service   conditions 147 

Shale  29 

"       oils    47 

Sheets,  10,  11,  13,  17,  23,  24,  33, 
66,  79,  82,  90,  97,  130, 
136. 
celluloid    .......  80,  82 

' '       fibrous    91 

' '       mica    107 

Shell   tortoise 83 

Shellac,  9,  11,  12,  25,  41,  42, 
47,  48,  49,  52,  66,  68, 
69,  70,  85,  86,  91,  94, 
98,  107. 

' '         compounds,  5,     9,     10, 
11,  87,  89, 
94. 
substitutes,  47,   83,   86 

' '         varnishes    52 

Short    circuiting. ..  70,  102,  147 
Shrinkage,  23,    53,    71,    72,    76, 
77,  96,  127,  153. 

Siberia    23 

Sierra  Leone 44 

Signal  parts 163 

Silica,  10,  16,  21,  23,  24,  25,  26, 
27,  29,  71,  73. 


' '       fused   75 

Silicates 10,  20,  24,  26,  33 

Silicious    material 30 

Silicon 25,  26 

Silver    59 

Silver  salt 59 

Sine   curve 176 

Slaked  lime 26 

Slate,   7,  14,  76,  165 

' '      waste   14 

Soapstone    15,  75 

Soap  works   59 

Soda 23 

Sodium   24 

"        carbonate 80 

' '        hydrate 26 

"        silicate    26,  76 

' '       sulfide   , .    35 

Softening   10,  106,  157 

Soja  bean  oil 50 

"        "     tree    50 

Soluble  silicate 26 

Solubility    35,  44 

Solvents,  13,  34,  45,  48,  50,  51, 

62,  69,  71,  79,  90. 
South  Africa 20 

"      America  .. 43,  52 

' '       Carolina 36 

Spinning 36 

Stamped   metal 169 

Starch    15,  49,  56,  59 

Steam    34,  115,  116 

1 <      tables    66 

1  i      process   54 

Stearic  acid 39 

Stearine   pitch 39 

Steel    HI 

Stick  lac 41 

Stinging  nettle 37 

Strain    101 

'  <       insulators  . .  . .  130 


206 


MOLDED    INSULATION 


Straw    32 

Strength   32,  75,  100 

1 '  mechanical,  18,  19,  22, 
78,  99,  101,  102,  106, 
129. 

"         tensile   101,  189 

Strengthening  medium 78 

Stress,  mechanical 102 

Structure.  .20,  21,  22,  23,  32,  33 

Sublimation    34 

Substance,   horny 13 

Sulphur..  12,  17,  38,  53,  54,  55 

Sumatra   45 

Sun  ray 68,  69 

Switch  base 169 

"       box 122 

"        handles    153 

Switzerland 38 

Synthetic  resinous  materials, 

11,  17,  63,  94,  99, 
101,  103,  105,  123, 
131,  139,  141,  143, 
147,  149,  151,  153, 
155. 


Talc   26 

Tanneries 59 

Taper    123,  129,  130 

Tapes    40 

Tapping    100 

Tar  oil   61 

Telephone   receivers 12 

Tensile  strength 101 

"        testing  machine.. .  .189 

Terpenes 34 

Tests,  172,  173,  175,  177,  178. 
179,  180,  181,  182,  183, 
184,  185,  186,  187,  188, 
189,  190,  191,  192. 

"       arc 190 

'  <       puncture   184 

lt      resistance   184 


Tetramethyl   —    diamidodi- 

Dhenylmethan 59 

Textile    . 42 

Thin  walls 121,  130 

Third   rail   insulators 163 

Threading   100,  127 

Tools    12,  107 

Tortoise  shell 83 

Toughness,  32,  45,  78,  82,  100. 
155. 

Transformer    176 

"  oil    ...179 

Transparent    82 

Trinidad  39 

Trioxymethylene   57,  59 

Tubes 17,  55,  97,  136 

Tung  oil 50 

Turf 15 

Turpentine   44,  46,  51,  56 

Tvrosin   .  .   60 


Underwriters    70,  104 

Unglazed    102 

United  States,  23,    29,    36,    38, 
153,  169. 

Upland    cotton :   36 

Urticacea? 37 


Vapors 132,  133 

' '       gasoline 132,  133 

oils    ...133 

Variation 97,  119,  125,  155 

Variation 97,    119,    125 

Vats    27 

Vegetable  fibres,  15,  32,  33,  36, 
37,  90,  95. 


INDEX 


207 


Vegetable  filler    14 

' '          gluten    15 

"          oil  39 

' '          substance    41 

' '         waxes 14,  15 

Venezuela    39 

Volcanic    origin 27 

Voltages  69,  70,  175 

Voltmeter 176 

Vibration 107,  134 

Virginia    37 

Vitrification    28 

Vulcanization    10,  53,  54 

Vulcanized  fibre 36,  37,  90 

"  products    107 

W 

Wall  box 123,  169 

Walls 123 

Warping 107 

Water,  10,  17,  22,  24,  26,  34, 
35,  38,  40,  41,  42,  44, 
52,  62,  64,  68,  73,  76, 
80,  81,  82,  84,  86,  89. 
91,  102,  103,  106,  115, 
116,  178,  183,  186. 

Waterglass 26 

Waterproof,  9,  18,  24,  89,  102, 
103,  104,  155,  163 


Waterproofing   media 72 

Waxes  51 

Wax,  sealing 120 

Weather  conditions.  ..  .69,  163 

West    Indies 36 

Wheels,  abrasive 109 

Wild  rubber    53 

Wood,  7,  9,  35,  60,  61,  99,  100, 
130,  153. 

alcohol    51 

<  <        fibre    35 

forms    13 

"        pulp,  11,   12,  31,  32,  35, 
88,  89. 


Ying-tzu-tung   50 


Zanzibar 44 

Zinc  compound    31,  58 

"      chloride    30,  64 

' '      chloride  solution 30 

' '     oxide    30 

' '      oxychloride 31 


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